Gpu clock stuck at 501 mhz on csgo and lol

Hardware GPU
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the only tabs i have open are facebook and twiter when playing, i play a game of lol and the clock speeds are at 1100 when in the game at the start with 150 fps, but then it drops to 501 after about 1 minute, my fps then drops down to 40. I just want a fix for this i dont know whats causing it :(

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bump

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What are your specs and temps?

Fill out your profile with specs so people can help you better.

24

have added them, my specs are: 

Windows 7 Ultimate 64-bit SP1
CPU
AMD FX-9370 5 °C
Vishera 32nm Technology
RAM
16.0GB Dual-Channel DDR3 @ 802MHz (11-11-11-28)
Motherboard
ASUSTeK COMPUTER INC. CROSSHAIR V FORMULA-Z (Socket 942) 27 °C
Graphics
K222HQL (1920x1080@60Hz)
ASUS VK222H (1680x1050@60Hz)
3072MB ATI AMD Radeon HD 7900 Series (ASUStek Computer Inc) 51 °C
Storage
931GB Seagate ST1000DM003-1CH162 ATA Device (SATA) 19 °C
931GB Western Digital WDC WD10EZEX-00KUWA0 ATA Device (SATA) 23 °C

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bump

26

still have the issue

27

Yeah dude had this same problem, a format and fresh install of windows helped me. Had it happen once again but I was overvoltage my gpu wich involves flashing the bios. I formatted again and since I haven't been messing around its been solid for the last 6 months.