Your 550 should be fine, but cutting it pretty close to not enough, the only reason is suggest going up to 650 is to compensate for any additional parts you have running, e.g. amount of harddrives, LED's, little things like that. As well as your CPU being pretty high end. I have pretty much the same specs but i run a 750 PSU.
The PSU could be causing the problem, have you tried running the PC in Safemode with Networking? You should be able to run a bot still, which will let you confirm if its hardware of software related