If the virus is affecting you from downloading any anti virus systems/open any programs at all, then shut your computer off and then put it into safe mode. (If you don't know how to put it into safe mode, all you do is restart your computer and when it's rebooting press f8 repeatedly.
After your in safe mode run a full system scan with an antifirus program such as avast. After the program has found the infected files, and removed them you should be fine.
I would also suggest for you to keep the anti-virus program to run regular checks from here on to avoid this type of situation from happening again in the future.