Brand new build, but freezes when strained

My specs: (built 24 hours ago)

Operating System
Windows 8.1 Pro 64-bit
CPU
AMD FX-9590
Vishera 32nm Technology
RAM
16.0GB Dual-Channel DDR3 @ 936MHz (13-13-13-32)
Motherboard
ASUSTeK COMPUTER INC. M5A97 R2.0 (Socket 942)
Graphics
SyncMaster (1680x1050@60Hz)
4096MB ATI AMD Radeon R9 200 Series (Sapphire/PCPartner)
Storage
55GB KINGSTON SV300S37A60G (SSD)
931GB Western Digital WDC WD10EZEX-08M2NA0 (SATA)
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My problem:
Whenever I run something strenuous on my computer, it freezes up. Ctrl+Alt+Del doesn't respond, mouse cursor doesn't move, and I can't even turn on/off my keyboard's LEDs. First, I was converting videos and surfing the internet at the same time, and it froze. It seemed like an anomaly at first, so I just did a hard reset, and continued with what I was doing, and then it froze again.

Seeing it happen a second time caused me to download a stress tester (Prime95 was the one I used), and I did a test on the RAM. It froze up after a minute of stress testing. When my build restarted I ran my check hardware program (Speccy) to check the RAM. The above Tech Specs are the copy/paste of what the program told me. You can see the frequency in underlined bold. The RAM is advertised for 2133 MHz.

My theory was that I had to manually up the RAM speed in Bios, which I tried. I selected 2133MHz, and saved/reset the computer. After giving me the ASUS screen, it only displayed a black screen instead of the usual log in form. After the next reset, I reverted the RAM speed and then booting was back to normal... but I'm still at risk for freezing.

Question:
Is my RAM the reason why I'm freezing or is it something else that my new build has a flaw in? Ask me any follow up question for more info. Thank you for the help.

You never mentioned PSU, that processor draws a lot of power (200W +) specially in turbo mode, R9 200 series, if it's 280, it draws a lot of power too, Next thing would be CPU temperatures, it's a HOT CPU, it deserves good water cooling for any practical purpose. As far as ram goes, 936 *2= 1872 so it's actually 1886 MHz memory, 2133 MHz would be overclocking and needs higher voltage than on standard frequency.
I would start with minimum manual settings for everything, no auto boost or power savings in BIOS, do some tests and than up components one by one by few MHz and keep tabs on temperatures and voltages.

My CPU has it's own liquid cooler and it hasn't exceeded 45C even in stress testing.

Good to know about the RAM, I did not know that.

My power supply is the Mod x stream-pro: 700w. I think this might be where the problem is, power might be allocated incorrectly. I'll take your advice with testing everything at minimum performance, and then increasing the MHz a little at a time. Any more advice?

Yes, check PSU by rails, most modular ones are multi rail and the rail (branch) for PCI express may not have enough Amps. Don't quote me but I think R9 280 needs at least 24 A to work under load. I have 660w PSU but it's only 18A per rail but is more than enough for my GPU. 8 pin for MB at 220 Watts means that it needs at least 18A on that rail. The rest of system doesn't need even close to those two "high spenders". That MB might have something like LLC (Load Level Calibration) setting in BIOS. For all practical purposes, it's a limit to what voltage and power to CPU may be delivered. Auto setting might have set it too low and it could be cutting power to CPU just when it needs it most. Have to be careful with it so it doesn't exceed processors highest allowable voltage.