have u OC'ed the card at all? i got hd 6870 a couple of months ago, and i didn't know much about OC'ing. So i cranked up the shaders and core to its max, and considering my card has no voltage control, it crashed straight away. I didn't read my GPU manual so i did not know u could reset the clocks to default at windows start up so i had to remove my GPU and uninstall CCC.
Anyway the point is, i tried reintalling CCC, but my pc crashed again so i assume that it somehow remembered my OC even though i uninstalled it, perhaps there was some registry file i didn't remove. Maybe this is happening for you?