Your PC not letting you open any programs isn't necessarily a virus. Have you tried, right-clicking and choosing "Run as Administrator?"
If you do have a virus, this program could help.
I would first recommend booting your PC into "Safe Mode." See if you can open your programs that way. If that still doesn't work, I would then recommend performing a system restore on your PC. If you don't know how to do these, please Google it. It's very simple and instructions depend on your OS version. There are YouTube videos which show how this is done too.
But, I would ALWAYS recommend having some type of AV software on your PC. You can lookup details on the different types of AV software out there: av-test.org