Unknown windows option pop-up

[weaver00]

Just today I have started my PC and get a normal boot until I get to the Background/wallpaper ( which loads normally), I then get a windows option box which has never appeared before. The small box has a title panel which is blank, in the body of the box is a yellow triangle with an exclamation mark, underneath are two rectangular buttons, one marked ‘yes’, the other marked ‘no’. I have no idea what it is asking, but when I press ‘yes’ or 'no' the programs load normally.
I have tried right click to find out what it is, I have enabled a boot log but get no mention of it, I have scanned for spyware, adware and malware, I have also booted inn ‘safe mode’ when it doesn’t appear.
Intel p4 3.0ghz, 2ghz ram Windows XP home sp2
Any ideas?
Thanks,
Robert Weaver

[glc]

Run msconfig and analyze all startup items. Also check the startup group in the start menu.

[weaver00]

I have checked through msconfig, and can find nothing out of the ordinary. Attached is what it looks like:-

Robert Weaver

[weaver00]

A brilliant little program called 'Autoruns' lists each event/action in order through the start up procedure. I was surprised at quite how many dll's were started but disabled them one at a time and got a clean boot when I disabled crypt32.dll.
Thanks for your help and suggestions.
Bob Weaver