Pc virus and malware removed but pc very slow now

Hi all and firstly great site and many thanks in advance for taking the time to read this and maybe help me. I came home yesterday to find my son at the pc almost crying, he had been on here looking for a keygen(kids dont learn) and had visited many warez sites, I had avira antivirus installed but through him downloading something a virus got through. avira wouldnt clean them and the pc was getting slower and slower so he installed bitdefender and spybot. He ran both of these and found a few viruses and some spyware which he thinks he has removed, he also tried registry cleaning software from coffee cup and deleted registry entries. Now the pc is even slower strugling to do even simple tasks. The viruses he listed are BDS/POISON.V.14, WORM/AUTORUN.OGA, TR/AGENT.27648.22, TR/DLDR.AGENT.AHCG, TR/VIRTL.PORTSCA.2, HEUR/HTML.MALWARE AND FRONTRA. I dont know what else to tell you other than when I close the pc it has a few error screens come up saying programs are trying to close etc, 1 being msnmessenger and another called secservice. Hope somebody out there can help. many regards Ray Smith