Hmmm Weird Restart Problem

[Avengeance]

I keep having problems with my computer that are really weird. Well recently I got a new motherboard (A8N SLI Premium) Everything went fine until a couple days ago it started restarting when I would load into windows. For some reason it stopped doing that and started working, and was working fine. Now all of the sudden today, without changing anything it started doing it again, and I still havent been able to figure it out. It happens when I click my login name and it starts to login to windows, it starts to load up some programs, then just restarts. And there is something wrong with my video cards (cause they are XFX's) to where if you restart them and dont let them sit for a few secconds (a real quick restart) they wont display a picture. That is just something else to add to my annoyances with my computer. Anyone know what this would be caused by? I thought it was the ram but I changed around the settings and it still does the same thing. I am going to keep looking in the BIOS but im not sure I will really find anything since it is so random. Also I dont think its a power problem because I have like a 550 (or 650w) power supply. Thank you!