I think this is a case for a Hijackthis log.
to get hijackthis, click here download it, and run it. it will produce a report of all non standard registry entries (IE potentially dodgy stuff) on your PC. Some of the repored entries are harmless (and may well be vital to the PC working right), and some of them may be the cause of your problem.
But it takes a real Expert, like Nellie2, to tell the difference. I would not have a clue.
You will need to post the report here, and hope Nellie2 comes along to see it.
The report will almost certianly be *far to big* to be posted here in one go (max 800 words at one time), so you may need to do it in two or three bits, and you will *have to* double spaced it so it reads right. ->
So a line from the Log,
then the next line.
Remember to include the header, so anyone reading it knows the version of Hijackthis being used.