Turn on computer crashes / powers off at the desktop

[Jekub]

My computer worked perfectly after I changed my PSU from a crappy one made by ace (520W) that came with my prebuilt system, to a corsair CX500M. Then it started crashing almost immediately at the desktop (6th May). Booting in safe mode fixed the problem but disabling all programs that started on start-up didn't, Taking my Nvidia 650ti Boost out and replacing it with a 610 fixed the problem, and running with only by boot SSD with the 650ti Boost in also fixed it. I posted this here but unfortunately didn't get a solution so I left the 610 in and continued using my PC normally. Maybe a week later it decided to not put out power to peripherals or output to a display so I took out the graphics card and got an error message saying "Warning: MAIN BIOS CHECKSUM ERROR!" I think that this either finished doing what it was doing and dumped me at the lockscreen or powered off and when turned on dumped me at the lockscreen. Either way it started working. Then a few days later I turned on my computer and it waited a while and turned off with no warning at the desktop, originally I thought that it was getting too hot, however all my fans were fine and my water pump was working. After a while of troubleshooting I managed to fix the problem by switching the twin kettle lead that was plugged into a nearby Xbox 360 and my PC for a single Kettle lead. This then worked for a few days and then started doing it again. At this point I was near certain my new PSU had had it and changed it for my old one and had the same problem.

 

I'm out of ideas please Help

 

Full System specs

System Specs

CPU - AMD FX 6300

GPU Nvidia 650ti Boost / 650

PSU Corsair CX500m / Ace 520W

MOBO Gigabyte GA78LMT-USB3

 

And Now it works! No changes have been made! - You are all so helpful!