Helping people with computers... one answer at a time.
We'll look at solutions for several reasons that could make the Taskbar and Start button disappear.
All of a sudden my taskbar is gone. I can't find it, so I have no Start button to click on, no quick launch start programs from - I can't even see what time it is! How do I get it back?
There are a couple of different ways that the task bar can disappear, or appear to disappear. Naturally the solutions are different, as are the workarounds.
Press CTRL+ESC. If your Taskbar magically reappears, then it's probably simply been resized too small, repositioned somewhere you didn't expect it, or perhaps it's beneath another application that's running full-screen on your computer.
The workaround? Press CTRL+ESC to access the Taskbar.
To fix it, this previous article, "My Taskbar is too small to be useful, what can I do?" includes a short video that shows the settings you can change to make it behave the way you want, and/or the approach to making it "big enough" once again.
If CTRL+ESC didn't make it come back, then the program that displays the task bar most likely isn't running. That program is often called the "Windows Shell", but it's really "explorer.exe". It's the program that not only displays the Taskbar, but also responds to the CTRL+ESC sequence.
The workaround: press CTRL+ALT+DEL to fire up the Task Manager. Now on the File menu, select New Task (Run...). Type in "explorer" and press OK. That should restart explorer and re-display your Taskbar.
In some cases that may not work, so we fall into the various approaches on fixing it.
If you don't have the Windows Shell running, you can still run programs as I described above: use Task Manager's File, New Task (Run...) to run the programs we need. I often like to run a command prompt, "cmd", as a quicker way to type in and run other programs from there.
My first recommendation is to run an up-to-date anti-virus and anti-spyware scan. Both viruses and spyware are known to occasionally interfere with the Windows Shell.
Then, I would run the system file checker, as outlined in this article: What is the System File Checker, and how do I run it?. That will check for missing or damaged files in Windows, and repair or replace those that it can.
Finally, you may be faced with re-installing Windows. You can perform what's called a "repair install" that will preserve your data. This article: "How should I reinstall Windows?" discusses that.
Now, naturally, there may be specific cases where a specific cause could result in a specific, simple, solution. In fact I'm sure that readers will comment with such various approaches. (Along the lines of "If you have this virus all you need do is twiddle that setting".) Those approaches may, or may not, resolve the entire problem. But if they make sense to you, then by all means try them out.
Microsoft also has a Knowledgebase article on the issue that includes even more steps to try: Taskbar Is Missing When You Log On to Windows.