PC FREEZES ON STARTUP

I’m working on a gateway essential amd 1000, 128mb ram, 40 gig wd hard drive. It was infected with numerous malware and viruses. It would not boot up. I lowlevel format and then tried to install windows 98 first. after the first reboot before windows finished installing, computer froze. things I did to fix- replaced ram, video card, pulled all pci cards out even before installing os. tried with windows ME also.same thing. ran diagnosics on system with diagnosics softer. shows everything ok.any ideas?