You say you have the drivers for the Quick Cam installed, I assume from the disk supplied with it? Go to the manufacturers websiste, they should have the latest one. Also, whilst you're at it, check your motherboard manual for the chipset make and type, go to the manufacturers website and get the latest drivers for that as well, and you may want to update your video drivers.

Believe it or not, ALL those are involved in the correct operation.

Failing that, download Ewido, you can get it from www.ewido.net/en, boot to safe mode and to a full scan, deleting what it finds, now reboot and try again, good luck, and let us know how you get on.