WIN98 REGISTRY CHECKER

Im working on a pc that has me stumped. It will operate flawlessly for some time, then out of the blue, the registry checker will come up on boot up.It says the registry has changed and windows will restore a good backup copy. When it re-boots the same message comes up and it will catch in a loop. The only way I can fix this is to start the windows install, which will repair the registry; then exit the set-up. Upon re-booting, everything will be fine – for a while. I have done extensive hardware testing, everthing seems ok. Configuration is PII 400, Gigabyte MB, 3D Prophet Video, S.B. PCI 128 sound card, Creative Modem (PCI), Kingston Network card (RealTek drivers), 64 MB Ram