My programs on windows 7 keep crashing out of nowhere?? HELP?

I don't know what's happening, it's the first time I use windows 7, i installed it saturday, it worked perfectly, yesterday i had no internet and avira antivirus scanned the computer and deleted a lot of exe cause it saw them viruses! Now many applications keep crashing! What do I do? Why does this happen? I got rid of avira cause I thought it fcks up my software but it still happens. Even winrar for god's sake! I reinstalled winrar 2 times cause it crashed on startup. My games have weird errors too, like, they're present in task manager at processes but they don't run. Or just freeze. What the fck is going on??? Is it a virus? I had almost no way to get a virus, since only now I got internet back and the cds I put in are clean.