Looks like your friend didn't know about commandments 4 & 5:
4. Thou shalt not connect to the internet without installing an antivirus, nor shalt thou begin a scan without checking for updates.
5. Thou shalt not connect to the internet without installing a firewall.
http://forum.avast.com/index.php?topic=17992.0Is this a new computer, or just newly connected to the net?
If it's new, it probably won't be worth trying to clean it: just restore it to factory settings and start again. as Tech has said.
This time, install an AV and a good firewall (ZA or Kerio) straight away, and update the computer at the MS update site, because even a new computer can have security vulnerabilities.
If you do want to try and clean it, Trend Micro Sysclean is the best thing to use, followed by McAfee Stinger, Ad-Aware and Spybot Search and Destroy.
After running these, see if avast! is responding and try a boot time scan.
Ewido is also worth running as Spiritsongs mentioned, if the computer is responding well enough to install it.
Finally, post a HijackThis! log so we can check that the computer really is clean.