7900 gt random freeze and random crash

so i was oc'ing my 7900's vmodded em oc'd em to like 700 and went to stress testing, the oddest thing happened, the computer not only froze but just shut off. it didn't hang or anything just shut down? so i brought the core down and was happily gaming till i upgraded to those new drivers the modded 97 series, now i've got random freezes that go away after a few seconds and random crashes as well? i've since went back to the old drivers buti 'm not sure the problem is gone, does anybody have any input on this??