My computer boots properly only when I have RAM in one of the slots on my motherboard. If I put both sticks in, regardless of the order, the computer turns and off again by itself repeatedly. I have a ASRock H77M motherboard, 2 8GB sticks of Patriot Viper 3 DDR3 RAM, a 550Ti Geforce GPU, an i5-3570K CPU, and a 450W Roswewill Capstone PSU.
When I originally built the computer, it worked properly for a couple of days with both sticks of RAM, until randomly crashing to blue screen. I found out one of the sticks was corrupted and so I sent them in for new ones.
I just reinstalled Windows 7 and added both sticks of RAM and I wasn't able to get the PC to turn on until I removed the stick from the second memory slot (its labeled B in my motherboard manual/ the farthest from the CPU). I think that the motherboard may be the issue but am hesitant to send it back until I know for sure.
Edit: the fans all turn on properly upon startup regardless, so I don't believe it to be heat-related.