I started exactly the same thread on here a few pages back, have a look.
I tried every solution offered by the kind people, but nothing helped. I even deleted my protection from my laptop and bought the best McAfee anti-everything I could find but it didnt help. I started to think it might be a hardware problem.
I then decided to pick up the phone book and find a local, back street pc repair shop (not pc world!!).
Told him my problem.....£35 for a complete clean up.
Machine is like new. Brilliant.