hi, i would first try a system restore back to a time before it started happening,if no change ,then i would would try running system file checker a few time .
go to start/run, type in SFC /SCANNOW , it may require yo uto have a windows cd i nthe drive to run sfc
This looks like it will solve your problem. I'm sorry that it is just another link to another forum, but I wouldn't like to try copying & pasting all that stuff here. Besides that guy deserves the credit.