If you have a virus try using AVG Free at
AVG Free Advisor - Free antivirus and anti-spyware downloads
You will 1st have to uninstall any other programs 1st and then download the AVG Free.
Had big probs with virus a while ago and the AVG one was the only one that detected the ones that caused the problems.
Other thing to look at if that does not fix it could be the power pack at the top of your computer.
Had problems opening pages, got a good 2nd hand one and fixed problem straight away.