Hi guys, I recently carried out some upgrading on my Alienware Aurora, including the SSD and some new SATA HD, as well as upgrading the cooling on my GPU's. See specs below:

ASUS PQ321Q 31.5-Inch 4K Monitor
Windows 8.1 64-bit
Intel® Core™ i7-4960X Processor Extreme Edition (6-cores, 15MB Cache, Overclocked up to 4.3 GHz) Liquid cooled
32GB DDR3 Quad Channel
2 x Sapphire R9 290X 4GB DDR5 Liquid cooled
2 x 2 TB SATA 6Gb/s (7200RPM) 32MB Cache
1 x Samsung 1TB 840 EVO 2.5" Solid State Drive
Alienware Aurora ALX Matte Black 875W Chassis

My question is, when I run 3DMark after about 30 seconds my system is rebooting.

What would be causing this? I am playing all new gen games on ultra, with no issues whatsoever. On the 3DMark, I have even tried reducing to 1,2 and 3k without any joy, it still reboots.