Problem Created By fully updated Antivirus

Hello,

i have encountered a problem in my pc that is i installed the new version of avira antivirus installed in my pc but the problem occur when i completed the complete scan of my pc , avira found a virus with the name Tr\CryptZpack worm in the following directory-C:\Program Files\Microsoft Common . Avira had quarantined it but when the next time i restarted my pc ,it did'nt display the desktop & startmenu and also the write click did'nt work so this was the serious problem for me . But there was only one thing was working-The Task manager after that i run a new task i.e., MY New Avira After running it i restored that suspicious file which was avira quarantined,So that my computer works as it was earlier.But it always hang in the middle of the execution of any program so still there was the same problem bcoz the virus exist in the "C:\Program Files\Microsoft Common" directory. I have updated my xp also but the problem did'nt solve. So please suggest me how to solve this problem ,what to do with this file or directory bcoz without it my pc is just like a dead.