What could be the reason behind the following stability issues

What could be the reason behind the following stability issues

Having assembled a new system from components believed to be compatible
the system in question does the following, seemingly at random:
often freezes (you have to hold the power button down to restart it), when
restarting it you'll simply get a black screen after the bios (again, hold
down restart button and try again), the system freezes and if you wait a
few minutes, it catches back up (i.e., if you were playing a video, the
video now will play at e.g., 2x speed until it gets back to where it
should be), Chromium browser will freeze or it will say "Waiting for
cache..."
The operating system is windows 7 and the build components are as follows:
SAMSUNG 840 Pro Series MZ-7PD128BW
G.SKILL Ripjaws X Series 16GB (2 x 8GB) 240-Pin DDR3 SDRAM DDR3 2133 (PC3
17000) Desktop Memory Model F3-2133C9D-16GXH
CORSAIR HX series HX650 650W ATX12V v2.2 / EPS12V 2.91
AMD FX-6300 FD6300WMHKBOX
EVGA GeForce GTX 760
ASRock 990FX Extreme4 Motherboard