Viruses!!!

could someone please tell me wat the heck is going on. i would greatly appreciate it. my friend has a pentium 4, 1.6 256 ram and 40g hard drive. i recently did a scan for viruses at trend micro. found a record breakin 107,000 viruses ranging from randex32-blaster worm-to welchia worm. i tried deleting all 107,000 viruses took way too long so decided to replace the hard drive. next day installed a 80g hard drive and replaced the memory to 512. installed Xp and antivirus (norton coporate and AVG) software. ran both antivirus. DETECTED NAVI VIRUS!!! aka Welchia32 worm!!! wat the heck is going on!?!?! its a new hard drive and memory. wat could possible be causin this. please help. the computer is connected to dsl and has no firewalls. could that be the cause?

I haven't researched the virus but it could be a boot sector virus, meaning that even with a new hard drive the virus will still appear.

If you did a scan with norton and avg that virus shoulda been placed in quarantine, if it hasnt been then research all the viruses that appear for a fix.

107 000 viruses is just mind boggling