jordi_b

Boot your pc with minimal hardware installed. remove DVD-drive, Hdisks. Just boot it with RAM & video adapter installed all at normal clocksettings. Boot into your bios and set your RAM specs to what they should be. Then reboot and perform some memory tests. if needed via utility bootdisk/cd. Good thing to do is to check if your PSU is working correctly. (I checked mine by listening to it when booting pc with min hardware and then with full install; I heard some weard sounds comming out of it) Could be PSU problem. Also possible that your problem comes simply from bad OC combinations. So maybe overclock in small steps and at every step perform some stability tests.
Have fun :-)