C1, C3, 68, 69, or C5 errors are usually related to memory or memory controller errors.

Try manually clearing the CMOS on the boards.  Refer to the board's documentation if you do not know how.  This can be done by moving a jumper on the board, or if the board has an onboard CMOS clear button, depress the button a couple of times.

Also try the sticks of RAM one by one in all of the slots to see if any of them are able to boot.  If they can boot, then make sure your RAM is set to the manufacturer's recommended defaults.   Then try two at a time, and so on. 

If you have an aftermarket heatsink, it may be too tight on the processor. Try either loosening the screws a bit, or try testing with the stock heatsink that came with your processor.

Please notice that if you have a P55, H55,  X58, or the SR-2 you MUST populate the Primary memory channel first, which is the non-black memory channels.

For more information on other POST codes review our FAQ here