Possible Spyware Threats need help

hello everyone, i’m pretty much new in the communauty, but i’m having some problem with a virus , my is the fact i download avast way back after the viruses spread inot my pc , blocking all my pc defensive modules and stuff , its like i’m no longer in command of the computer and i’m just a third party , all the background systems are under his control , cannot access control panel nore do “add/remove programs”