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. 

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.