Computer lagging and freezing and sometimes restarting suddenly

[LULZOR]

My computer randomly freezes with a weird buzzing sound(if theres audio playing else it just freezes) for a sec or so before continuing normally. sometimes it just restarts itself without warning no bsod or any other warning. while playing games like dota 2, the game sometime crashes to desktop again with no warning, it just closes. other times the screen goes black and it freezes, although i can open task manager the game is normally not responding. the weird part is that all these problems just happened randomly one day after i went away for about a week. i come back and suddenly everything is screwed up, it was working fine for the last 2 years. so far i've tried updating drivers, uninstalling ide ata/atapi in device manager, changing the power plan settings, memtest check, checkdisk but all have failed. I'm pretty desperate at this point so any help is appreciated thanks
example of buzzing and freezing is something like this https://www.youtube.com/watch?v=CF9Pvdsz0UM

 

[huilun02]

While you were away was there anyone at home who could have knocked something loose? Check all your cable connections.

Is your CPU/GPU overclocked? Are temperatures ok?

 

[LULZOR]

oh yeah forgot to add, yeah i've been monitoring my temps and cpu rarely goes above 55 degree c and gpu never above 70. cpu (i5 3570k) and gpu(r9 290) both at stock settings . Nothing seems lose also

 

[huilun02]

Do these

http://www.speed-up-pc.org/speed_up_hardware/chkdsk_utility.php

http://www.sevenforums.com/tutorials/715-memory-diagnostics-tool.html

 

[LULZOR]

did both, no problems found

 

[huilun02]

Then its probably something failing. No idea what though.

 

[LULZOR]

any rough ideas?