It might not be the load causing the problem, but could have just failed... it does happen.
I have an OCZ StealthXStream (I think) power supply which started doing something similar to yours. You could power the machine on and it'd work for about 30 seconds.. might start to boot Windows, or just get into Windows before turning off. Then would turn on again and keep doing the same thing. Even if you went into the BIOS, it'd still just reset.
Tested with a spare PSU from work and found it was indeed faulty.. worked fine with the new PSU. Luckily it turned out to be under a 3 year extended warranty with OCZ and it was about 2 years old so I was able to send it back and get a brand new one off them - no problems so far!
I was running that board, the quad core CPU, Palit GeForce GTX 560 OC, SSD, 1TB 7200RPM HDD, and PCI-e sound card (which needed a molex connection for additional power) off that 500W OCZ power supply for years so your 600W enermax should be more than up to it!
Anyway - glad you got to the bottom of it.. even if it does mean a bit more expense!