Question Pc became slow suddenly

[Boy with Brain]

Hello, I got a workstation pc from a friend who used it for intensive tasks. after few months i have encountered a issue that it has became much slower than usual and now its unusable. Before this problem YouTube videos used to be played smoothly at 4k but now it gets laggy, choppy and the audio distorts in intervals while watching the video, i used to get 180 fps in csgo but now it even struggles to get 20 fps. This used to happen before too but after and reboot it used to get fixed but but after an power outage it has became permanent. I thought it was a hdd or ram problem so I ran chkdsk test, and ran even sfc/scan to check for system corruption and ran dell diagnostic tool in bios but it did not work. i have even checked for virus or malware in my pc but none were found. i don't know if this issue is related to an error which pops up before booting called "correctable memory error". I have reinstalled windows too please help me anyone

specs
Intel Xeon E5-1650 v3 3.50ghz
total ram 48gb (6 sticks of 8gb ddr4 2133 mhz ecc memory)
nvidia quadro K2200
2x ToshibaDTO1ACA2000 2tb
dell precison tower 5810

I don't use the second drive, if it can help to solve the problem I am ready to use it.
I have a bootable usb and media installation if it can help.

 

[Lutfij]

Welcome to the forums, newcomer!

If you're working with Microsoft's Windows OS, what sort of resource usages are you seeing when the system boots to OS GUI and is at idle? Make and model of the PSU in your prebuilt? Age of the PSU in question?

 

[Boy with Brain]

Thanks for your greeting
Yeah windows 10, my cpu usage and hdd usage becomes very high. Resource usage is normal when it's idle and when it boots but when do any activity the same issue arises. Psu model-dell 685w power supply for dell precision tower 5810 workstation. Power supply is from dell and it's 10 years old