|Why would you think changing the OS would fix a power problem?|
Did you check the CPU temp to see if it's overheating? It could be shutting down to prevent itself from frying completely. I believe that board is from a Gateway / eMachines - why did you not post the model number of your system? And what about the power supply? Which did you have & which one did you upgrade to? Please list the make/model, wattage & amperage specs to both units. eMachines are notorious for using crappy Bestec units, hopefully you didn't buy an identical replacement.