Closing window reboots machine

[normanallen]

This is something that has only started happening over the last few days.
Sometimes when closing a window using the red X (top right corner) the computer reboots.
This is XP SP2. I have run Ad-Aware and SpyBot S & D, which found a few things but apparently it is still happening.
Just as a curious thing, some web sites simply won't load. For example I can see Sky News, but Sky Sports won't load. This happens both in IE6 and Firefox 2.
Also, I had it happen to me when I used the File/Close menu on RealArcade, so it's not just the red X that's affected.
Nasty.
Any suggestions?
And I couldn't access the DaniWeb site either, so this is coming from my office machine!!!

[normanallen]

This is something that has only started happening over the last few days.
Sometimes when closing a window using the red X (top right corner) the computer reboots.
This is XP SP2. I have run Ad-Aware and SpyBot S & D, which found a few things but apparently it is still happening.
Just as a curious thing, some web sites simply won't load. For example I can see Sky News, but Sky Sports won't load. This happens both in IE6 and Firefox 2.
Also, I had it happen to me when I used the File/Close menu on RealArcade, so it's not just the red X that's affected.
Nasty.
Any suggestions?
And I couldn't access the DaniWeb site either, so this is coming from my office machine!!!

Very bad that I have to solve it myself! When I went log in last night my SpySweeper splash screen wouldn't go away. I've removed it, and reinstalled it, and everything looks back to normal (I hope).
Strange behaviour from a "safe" program.