Blaster and the many variants exploit a buffer overflow vulnerability. However, if the incorrect sequence is used, it causes the RPC process to shutdown, exactly like what you are getting. Therefore, your pc isn't infected, its trying to be infected, but the virus is trying to use methods for say, SP1 or win2k on your SP2 machine. Best option is to install a firewall and block all incoming ports. Then head to windowsupdate and install everything
Cheers
Glipsie
Cheers
Glipsie