Unknown performance drop

[Protocnik]

So over last few months, my computer's performance significantly decreased. It was working good for 4 years and now i have no idea what to do.
If i play a game, there is always FPS drop every few sec and when i watch movies sometimes screen freezes for short duration.

my specs:
HD 5870 1Gb
AMD phenom x6 II 2.8 Ghz
4Gb ram
GA-MA770T-UD3

I tried to change GPU and RAM, but problem was still here. It might helped abit
changed with R9 280 and 8Gb ram

And sometimes when i check task manager, disk is at 100% use for unknwn reason.
Anyone knows what is wrong?

Thanks for help in advance.

 

[badboyrog2]

change everythings