I had similar case. PC-Check said that everything is ok but everytime I connected internet or sometimes when logging on to machine freezed. I made new windows installation -> no help, then try change every part in computer to another (except motherboard) -> no help after that I tried to using IDE drive (before used sata) -> it helped, I think SATA chip broken. But I can't understand why It freezed computer especially when connected to internet. weird!