Hey, i have problem with my system! please check this out

Walinen

Distinguished
Sep 9, 2013
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My specs:
GIGABYTE GTX760 2GB GDDR5 OC Rev 2.0
ZALMAN Z9 U3 3x120MM FAN CONTROL USB3.0 ATX
AMD FX-8320 8-CORE 3.5G 16M AM3+ 125W BLACK EDITION
ASUS M5A97 R2.0 AM3+ AMD970 DDR3 USB3 SATA6 ATX
AXP 750Wats, cheapest model on internet! i bet its not even close to 700w
4GB ram of my last computer, nothing special
CPU cooler: thermalright hr-02 macho rev.a

I builded this pc couple weeks ago and haven't got time rly to play anything else than lol
But now started everyones voices, example in skype calls, i hear voice with anoying disturbion like the voice got cut into pieces, this happens sometimes in games too

Now donwload world of warcraft, i worked for 10sec at ultra with good fps but then it dropped down to 2-5fps and wasnt going back
Worked after second try but haven't tried more

I'm playing diablo at 200fps and game still lags, same way that my worldofwacraft did, not as much bu still, fps doesnt drop it just feels laggy

Not played youtube video with 1080p and video fps turned to 2-4 and i heared sound of the video by parts and anyoing disturbiance. Any clues or do i have to pay for computer repair what checks all the parts ?