Random freeze while playing DOTA 2, watching youtube videos (Error 41)

Hey guys, I've had this really persistent "freezing" problem with my PC from 'June 2012', now I've tried to solve it to the best of my knowledge regarding these issues but it just won't go away.

So what happens is: my PC freezes randomly for no reason while I'm watching youtube videos or playing DOTA 2. It doesn't occur all the time and I can't replicate the freeze because of that... but here's what happens:

1. PC freezes randomly, at DOTA 2 loading screen. It's right after all the players have accepted to play in the found match (find match process) and the game takes us to the loading screen (loading resources and stuff I presume) now this is where my PC freezes. It's happened many times from June and sometimes it's happened as much as 3 times in a row and sometimes it doesn't happen at all for quite a few matches.

2. Rare PC freeze after DOTA 2 match is either won or lost and the game is about to show the players the score screen. This happens occasionally and is very much the same freeze as the loading screen one.

3. Freeze while watching Youtube videos, no specific types of videos (eg: captions, HD, 240p) but it happens just as much as the freezes that occur during the DOTA 2 loading screen.

*Note - After the freeze everything inside my cabinet from the PSU to CPU seems to be working/running/ON just as if it were doing so normally and I have to reset my PC manually at which point it completely powers down for a few seconds and then restarts with the "didn't shut down properly..." screen (this happens every time.)

Any help regarding this issue and how to fix it would be much appreciated. I don't know what's causing it.

I know that you are not talking about a BSOD, but if you post it following the Blue Screen of Death (BSOD) Posting Instructions, we may have a closer look at your system.

Nothing is wrong there .... as far as I can see.

For DOTA2, you may change the game's settings. Sit rextures etc to low or normal, not to high.

For youtube, disable hardware acceleration in your browser.
Firefox.
Chrome
Internet Explorer.

Are you overclocking? If so, set the clocks to default.

still not working :/ I just experienced 3 freezes in the past 3 hours