It also sounds like it could be a confilct in the system somewhere.
Maybe 2 or more applications tryiing to access the same memory address.
If nothing else works, how about trying to re-install or repair
Windows from a setup CD?
I would try the repair option first, just follow the on-screen instructions.
There is a guide for that here:
http://support.microsoft.com/kb/314058
To use the
Windows Recovery Console, you would probably have to run setup from a bootable
Windows setup CD, then choose an installation option from the boot menu.
But if you have it installed already, then you can just run it as
Windows starts up normally.
There are a couple of ways to re-install
Windows.
Either onto a new partiton, or even an existing
Windows OS partiton, without losing your data, it depends on how you do it.
The second method is not really recommended, but I've done it for years without any problems.
You could, for example, install a new version of
Windows, into an installation folder called
Windows1, for example, or install it onto a new partiton, it's up to you.
Good luck with it.