I had the exact same problem, nothing that I was directed to do by hp(the company I bought the machine from) worked, this included 3 send ins(for diagnostics) one of which replaced a faulty harddrive, and no that did not resolve the issue, plus numerous user end solutions which failed to produce the desired result.
I have been a 2 year long advocate of this program.. ultimately I was forced to switch antivirus brands, because of this problem.
and there is a problem, because several people I know who have the same edition of windows vista(64bit) have reported the same issue to me.