(I posted this in Memory originally but now have confirmed that not a RAM issue so am re-posting in Motherboard/PSU)
Motherboard: ASUS P7P55D-E LX
PSU: Corsair 700W
When I press the case power switch, CPU and Case fans spin for about a second before turning off, and then about 5 seconds later the whole system comes on, boots BIOS and into Windows 7 just fine, but as soon as I open an application like Photoshop, the system blacks out and reboots.
I left it running for 3 hours with just Windows running and it stayed on the whole time.
The issue first arose when I installed some new memory (increased from 2x2GB DIMMs to 4x4GB DIMMS). I have since tested 1 stick each of both the new AND original memory, same issue happening.
How do I test if something on my motherboard may have gone out vs something wrong with the PSU?
Since both are rather involved to unhook/hook up I am trying to rule things out before tearing the system apart.
Update: Instead of going with a new PSU I first tried using the motherboard's MemOK! on-board switch which (as I learned from the manual today), if you hold it down until the light comes on after booting up the computer, the motherboard will run a quick sequence of tests to determine proper compatibility settings. Did it first with the old 2 x 2GB sticks and had success (both in stability while running and having that weird false-start stop happening), now have new 4 x 4GB sticks in there and so far it is running multiple programs and going strong.
So, solved. I should have read the manual more clearly. Who'd have thought...