Helping people with computers... one answer at a time.
"The Windows Installer Service could not be accessed" is a frustrating error with many causes. I'll look at one trick that may clear a few of them up.
My OS is Windows Vista. Every time when installing a program that uses Windows Installer, I receive a message like this: The Windows Installer Service could not be accessed. This can occur if the Windows Installer is not correctly installed. Contact your support personnel for assistance. Do you know any reason why this is happening and what have to be done?
Unfortunately, the situation can occur for several different reasons - some of which are understood and some of which are not.
As a result, I don't have the answer, but...
I do have something to try. Something that I have heard that can help get past the situation in many cases and should work in Windows XP, Windows Vista, and Windows 7.
The theory is that the Windows installer has become confused somehow by the previous installation. Perhaps that installation crashed, perhaps the installation was aborted, or perhaps it simply finished and failed to finish cleanly. Regardless, the Windows installer is in a confused state and unwilling to accept further installations.
One approach to clearing the confusion is to, for lack of a better term, "whack it upside the head" by turning it off completely.
Right-click on Computer or My Computer, click Manage, expand Services and applications, then click Services.
In the list that appears to the right, scroll down until you see Windows Installer. Right-click on that and then click on Properties.
The Startup type listed will be either manual or automatic.
Change it to Disabled and click OK.
Reboot your computer.
Repeat the steps above, but this time, change Startup type from Disabled to Manual.
You do not need to reboot your computer here.
Now, try installing something and see what happens.
The theory is that forcing Windows to restart with the Windows installer service disabled causes some of the confusion about its state to be reset.
And once reset, Windows installer can be used again.
As I said, this may not fix every Windows installer "could not be accessed" problem, but it's a simple trick that can clear many confused situations.