first off, clean up the junk and clutter on the system as a first step....download and install Cleanup!
It will get rid of any malware which may be hiding in your temp folders (a common hiding place). You will also regain a massive amount of disk space.
Check 'options' to customize your settings, and then make sure only the following are checked:
1. Cleanup all user profiles
2. Delete prefetch files
3. Empty the recycle bins.
When Cleanup! is finished, it will ask you if want to log off and reboot. Answer NO
Further info, read the BP Cleanup! Tutorial