I've got the same exact problem with EVGA 780i board and Crucial Ballistix DDR2 800Mhz RAM. I've got 2 x 2GB sticks which I set at 4-4-4-12 @ 2.2v. Been running this rig for almost two months, originally I had everything at stock and it worked fine. Overclocked over a month ago: Intel E8400 @ 3.6Ghz, tightened the timings on the RAM (running at 1.8v for a while, then at 2.1v and finally at 2.2v for a few weeks). Running FSB @ 1600Mhz linked/synced with RAM. Everything was running good for a couple of weeks. Then I started having random stalls/freezes. Its started when I was playing Assassins Creed the other night. I had some similar issues when I first put together the rig (at stock speeds) with the PC totally freezing during games. After tweaking things I thought I had fixed it.
Then last night I left the PC alone for a while and when I came back the screen was black and nothing I did would bring it back. This is like the 3rd or 4th time this happened (PC refused to come back from screensaver/power saver mode). Note, I did *not* set it to standby/sleep. It just turns the monitor off after 30 minutes but then the monitor will not return. Anyway, I did a hard reset as there was nothing else left to do. Upon rebooting there was still nothing on the screen at all, plus I hear a loud beep with the "C1" error message. Tried reseting the BIOS jumper and that didn't help. I cannot turn my computer on, the mobo does not POST at all, it just beeps. I am going to try testing the RAM if I can. I read reviews (on new egg) about the Crucial Ballastix RAM being crap and I didn't believe it. It really sounds like its a RAM issue, which is not so bad. Much easier to replace then a busted mobo.