Explorer Error

[degradation]

I turned on my old computer yesterday and I decided to defrag it cuz its been a long time since its been defragged. So anyway, now when i turn on the computer, as soon as it loads up and is on the desktop screen, i get an error message. It says something like:

Explorer has performed an illegal operation and will be shut down

And then I can click either "Close" or "Details". Everytime I click "close", the message keeps popping back up. If anyone can help me out, that would be greatly appreciated.

[Tom]

Howdy degredation,
Could you post back here what you see when you click details? Let's see what you've got to work with for ideas to repair it.