From the information you have supplied no one can give you any specific fix.
Post a detailed report
Go to:- www.majorgeeks.com/download3155.html download and run Hijack this. “Do not try to do any repairs yourself.” Save the report and send it with your next post along with any error logs.
To check error logs, go to “START” “RUN” type “eventvwr.msc” Click “OK” and check if there any errors in the logs. Include any information that could help:-
1. What were you doing on the PC when the problem occurred?
2. Does it happen every time you do this?
3. What progs are running as well?
4. What have you done to fix this problem?
5. How long has the problem been happening?
6. Have you installed/uninstalled or updated any progs recently?
7. Any other information that may help resolve your problem. Remember, no one here can see your PC; you are the only one that can tell someone else about the problem.