Possible virus, how to find it?

Ahhh! I think I might have a virus on my pc, I've scanned the whole computer and it says there are no threats and any possible threats have been removed. However, my pc's performance is not good and sometimes whilst on the net all of my desktop icons dissappear! Help! I don't know what to do!!!

ouch...go to ccleaner.com download the latest version of the software (its free)..and do two things, forst analyze all the issues and then run the cleaner..once that is done click on registry (left hand side) and scan for issues and then fix the issues (everything is done automatically..really easyyy)..oh and by the way, no need to back up the registry. this little free software is awesome!!! let me know if that solves your problem a bit..if not ill give you some more advice!