GTX 660 problem FPS drops heavily

[twunicals]

Hey everyone,
I'm new to making threads and dealing with computers as im learning.
i have a Galaxy GTX 660 bought about 1 year and a few months, recently my computer suddenly shut downed for no reason while playing Counterstrike.
I roughly had 300FPS on Counter strike, now im on 120FPS with bad drops to 20-30, i currently cant play any games on it as it is really choppy

i changed my graphics card to a 750 (my older one) and now i have stable 50-60 FPS with no bad drops at all.
i was wondering if my card just overheated or what
i really need help on this.

extra info
i5-4690 CPU
H87 motherboard
8GB Ram hyperX
coolermaster V550

 

[twunicals]

Bump, i really need help

 

[ThroughTheGame]

Bump, i really need help

If you had in BIOS the option of "Spread Spectrum" in Frequency and Voltage turn it off. Maybe, by shutting down the bios reseted and Spread Spectrum turned on. Happened to me. Also, you can check if the GPU is running at full speed with GPU-Z.