Help, System under attack

I am working on a system running windows XP that lost several files and folders, It still boots but nothing will really run. I have run Norton AV and Trend micro AV but nothing is found. The drive shows 11 GB used in properties but when I select all in the C directory it only shows 6 GB used. I also found a file in the Program Files directory with a named of “zero, 7 squares, a period and 3 more squares” that has no properties. Also the Common Files icon in the same directory has an unknown type Icon, properties show it as a file but I can’t open and the size is 32.0 kb. It looks like most of the damage is in the Program Files directory and looks like virus activity to me, but Antivirus won’t find anything. Any help is appreciated.