clear the cmos
Just incase you don't know, To clear the CMOS you have to unplug the power and remove the battery from the motherboard, Leave it for 5-10 minutes(although I usually get away with 1 minute or so) and then try rebooting, you should now be able to get into bios and all settings should be at default, I'm not sure if the CCC changed the clocks over properly(I.E. overclocks every boot) so you may still have to go into safemode.
As a side note, I dont know if the ASUS 5870 has it, but some cards also have a 'safe mode' feature on them. this may take some investigating. ::Starts investigating::
EDIT: Upon review you may have to use the Operating system disk to repair windows boot.