Computer randomly freeze/hungs up at radom intervals - Forces Reset

Hey I have been having this problem for the past few months;

My PC will just freeze, everything become unresponsive and I am forced to reset the PC.
This happens at a random time, can be anything from 5 min to a few days after I turn my PC on this will happen - if I am watching a video or playing a game the audio will still transmit for about 10-20 more seconds then will start looping/stalling

This problem has happened the most while watching videos/movies etc on my media player (i have tried multiple media players, will still get the same problem)
It has happened about 2-3 times while playing games

I have tried a few things that I got from google searching this problem

Replaced my SATA cable from mobo to HHD.
Replace my HHD with a brand new one. (I have two HDD now - one is no longer connected, specifically the old drive)
Multiple fresh installs thinking that there was a file conflict.

I actually do not know what to do at this point - I have a feeling that there could be something wrong with my mobo, but as I am a uni student I do not have the funds to go out and buy a new one to test this theory.

If anyone else has ANY suggestion or even better A SOLUTION to this problem, please do tell.

Side note - when I was checking my my system info I noticed that there was a something wrong with my RAM - its says i have 16gb installed but only 13.4gb available (http://puu.sh/gGkkw/229726295c.png)
Just cheeking, does that mean my RAM chips might be damaged and need replacing?

Hello,
I see in your system specs that you are using an ATI R9 290x.
My bet is that your Vcard is the culprit, specially since you mention that it happens mostly when watching videos.
The issue has to do with Power States and the shift between idling with 2d clocks and jumping back to active 3d clocks...
Depending on the card, people have reported fixes with BIOS updates, etc. Since my card didn't have a new BIOS available, my fix involved OC'ing the 2D clocks by 1.5x the idle speeds (300mhz to 450mhz) using Asus GPU Tweak and slightly upping the Vcore Voltage using MSI's Afterburner.
I struggled with mine for weeks on end, but this finally fixed the issue for me (no freezes for a few months.)
Check out the Sapphire forum post on the subject. There are some very helpful folks there with a lot of experiences similar to yours. Several other threads are available for various cards, ie. the 4 gb vs. 8 gb versions.
The solution is in sight!
Regards-

I took a look-see at the link you gave me, sounded like exactly what I have been experiencing, so now I have downgraded to v14.9 and changed my voltage - Cheers for the link John
So far it looks good, no random freeze time.

Awesome- Glad to hear it.