Summary: Most laptops include a VGA or DVI connection for an external monitor. Setting it up is relatively easy, if you know the tricks and have patience.
How do I hook up a monitor to my laptop? I can not get the monitor to work.
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I see people struggle with this all the time. It's actually somewhat frustrating, since the answers are actually simple, just not obvious.
You need to know the magic keystroke.
And you need patience. Just a few seconds worth, but you absolutely need it.
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Most laptops built today include an external monitor connection. Most are VGA, but some are starting to include DVI digital video connections instead.

The back of my Dell laptop, highlighting the VGA connector.
The 'trick', if you want to call it that, is that they are not enabled by default. You need to take action to send video out that port. Typically, and this varies from laptop to laptop, there is a keystroke that does exactly that.

The CRT/LCD selection key on my Dell Laptop
Unfortunately, it's not a simple as turning it on or off.
First, realize that in order to enable the CRT/LCD keystroke you typically need to be holding down an additional key; on my Dell it's a blue "Fn" key. It operates very much like CTRL or SHIFT, in that you hold it down to enable the blue functions that are printed on the key tops. So in my case it's Fn + CRT/LCD to enable the external monitor.
Second, realize that it's not on/off. Pressing the key repeatedly cycles though a series of combinations. For example, each time you press that key, you may cycle through these combinations:
LCD (laptop screen) only, the CRT (external screen) is off.
CRT only, the LCD is off.
LCD and CRT both on, and displaying the same thing on both screens.
LCD and CRT both on, but displaying different things - together they form a larger virtual desktop where the LCD might be displaying the right side, and the CRT the left.
When you type the keystroke, the configuration changes to the next one in the list; when you reach the last, it starts over at the beginning.
Your list of configurations or combinations may be different, or in a different order. There is no standard, and each laptop may be different.
Third, and this is perhaps most important because it's the source of much frustration, it can take up to 5 or even 10 seconds for each new setting to take. And 5-10 seconds is a long time when you're standing in front of people trying to ready your presentation. I continually see people get very frustrated when they try, wait one second and assume that because it didn't work instantly it didn't work at all, and keep trying thinking that nothing's working.
If you take nothing else from this article take this: after typing the keystroke to change your LCD/CRT configuration, give the new combination at least 5 seconds to take before you decide it didn't work. Be patient. There are several hardware related reasons for this; most typically the time it takes your CRT or projector to 'sync up' to the signal that it's suddenly receiving.
The last combination where both your laptop screen and your CRT are on and displaying two different portions of a single virtual desktop warrants a little more clarification.
The likelihood of the LCD and the CRT being the same resolution or "size" in pixels is very low. You can see this when you look at the display settings in Windows:

You can see that while my laptop's LCD is 1440x900, the CRT/VGA output is set to 800x600. While you can often change the resolution of the VGA output, it's unlikely that you'll be able to match the native resolution of your LCD. The result is what you see - a virtual desktop that's not a perfect rectangle. That's something you simply need to be aware of as you move applications between the two for your display.
I'll admit that it can be a little frustrating at first to get the hang of how your laptop handles external monitors and how those external monitors react, but once you do you'll find that the external VGA output on your laptop might be one of its most important features. Just ask anyone who's made presentations in front of an audience.
Related:
Can I use my TV as a second monitor? Your TV can often be used as a second monitor, but unless you have a newer digital TV, the results will likely be very disappointing.
How do I set up a system with more than one screen? Putting more than one display device or monitor on your PC is relatively easy these days. With the right hardware you can create huge virtual desktops.
Why do picture colors vary from computer to computer, or when I print them? Color matching from device to device is difficult. Most monitors are not well calibrated initially, but doing so can return excellent results.
Article C3570 - November 22, 2008
To Dan:
Posted by: Doug Proctor at November 26, 2008 10:59 AMI choose not to go with Vista when I purchased a PC in June 2008, but I had to build it and purchase XP software. This is - and should continue to be - an option, and it just isn't that hard to build one.
Doug
A new connection for an external monitor is starting to appear called a Display Port. This is an interesting article on the topic.
Posted by: Michael Horowitz at November 26, 2008 1:19 PMhttp://lenovoblogs.com/insidethebox/?p=161
To Richard Deem
Yep! When I close and reopen the lid, the monitor is resized to the laptop screen size. I have XP.
To Doug Proctor
Keeping XP on a new machine is an option but I guess I'll go for Vista since I develop free/sharewares apps. For the moment, I give them to my friend to test on his Vista box. Getting Vista would make me independent. He has the highest Vista version (I don't know the name) but given the trouble he is having with it, I'd appreciate comments on the best Vista version for my purpose (just an Internet, office and development machine.
To Michael Horowitz
Great link. Thanks!
Lastly, how about connecting an external keyboard to a Dell Inspiron? I have 2 spare keyboards but couldn't find a suitable connector on the laptop.
Dan
Posted by: Dan at November 27, 2008 6:57 AMVista should also be aware that Presentation Settings behavior may be masking another problem. The graphics card probably has software that controls some of the same things that PS does. In my case, updating the driver for my NVIDIA graphics card and then using the NVIDIA Control Panel (accessed by right-clicking on a blank part of the desktop) solved my problem. Now setting up an external monitor is easy and reliable.
Posted by: Stuart at November 29, 2008 8:13 PMuhh i pluged in the cable into my toshiba laptop and put the cable into the samsung tv useing the vga cord.
it starts up fine but then it just cuts off... i don't use a dell so i don't know where the crt/lcd botton is it's just alot of pictrues which i don't know what they mean at the f1 f2 f3 ect. thing. i have found the fn botton though. the resilution is correct too.
if you could help me that would be great i really looked forward to playing on the big screen. anyways thank you if you could help me.I'm going to keep trying through trial and error but if you could get back to me thats great
30-Nov-2008
They do make external video cards for laptops as well. They connect to USB and provide analog or digital video. I have an Aluratek model UAV 100F.
Posted by: David Irwin at December 1, 2008 1:24 PMTo: Jom
My AcerNote light laptop uses Fn key + F1 to show what F key to use with the Fn key.
Posted by: Ed Vance at December 6, 2008 4:11 PMI have read all yoiur advise, however here is my problem...I have a laptop OPS as windows vista. I hooked up the correct cable to my tv and plugged it into the port on my laptop. It acts like it wants to switch but says no signal. I am sure all I need to know is what "magic" key/keys to press to make the change. It worked once and I cannot remember what I did. I don't have a fn key CRT/LCD to press.How do I make the switch.
Posted by: jo mills at December 10, 2008 5:32 PMI am so frustrated.
Thank you Jo
How can I use the laptop as a desktop? When I try to close the lid on my Dell laptop the monitor goes dark.?
Posted by: dave macheca at January 10, 2009 3:19 PMi have tried fn and the f8 combination sometimes it work an sometimes not
Posted by: tony at April 7, 2009 6:09 PM