[SOLVED] Why has my GPU's performance decreased suddenly ?

[Qreken]

I have an old school pc which I still use to play games but two days ago after playing project cars 3(working fine like 60@medium 1080p), I turned off my pc and turned on again after few hours but when I started the same title with same settings, fps dropped, like 30 to 35. I also tried others games but was same with other games too. But when I over clocked the gpu, it attained the performance close to previous ones but not exactly the same. Can any one help me to find out the problem.
Specs:
i7-2600
Rx 470 4gb
8gb ram

 

[Ralston18]

Update your post to include full system hardware specs and OS information.

Include PSU: make, model, wattage, age, condition.

Look in Resource Monitor and Task Manager to determine what is using the GPU? (Use both tools but only one at a time.) Check other resources as well - just as a matter of elimination.

My thought is that PSU may be nearing its designed EOL (End of Life) and no longer able to steadily meet the computer's gaming power requirements.