My pc fps dropped after a while

A long time ago when I got this pc and started playing csgo with it ,and I had a lot of fps but I stopped playing for 1 week and the fps started to be the same but when I got close to smokes they just suddently dropped and for a time to time breakes . Man it used to play csgo with so mutch fps why did they started dropping pls help.
laptop specs:
Intel(R) Core(TM) i7-5500U CPU @ 2.40 Hz
8,00 GB of RAM
64 bit
And yeah sometimes a bluescreen happends for no reason even in google but its rly rare to this happend
 
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