Weird PC issue - no one knows how to solve it

Hello, i looked for a fitting subreddit to ask about this and this one seemed to match the most. I dont have good knowledge about computers but I asked people who actually know alot about them and they don't know what to do either.

My PC screen randomly goes black and changes to grey and repeats it - i cant perfom any action. Using the shortcut for resetting the graphic card doesnt help either. After this happens, im forced to unplug the power cable to reset the pc - it always works, but i know its unhealthy for pc.

What i know:

-After this happens, i can hear all sounds (spotify discord etc. But no one can hear me.

-This happens mostly while alttabing or a game window pops up.

-This happens on both of my monitors.

• I have this issue at least once per 2 weeks. (Using pc daily)

-Cleaning the pc helped for a short amount of time (it started happening again about 25 days later)

-The graphic card's fans seem to work fine.

All i got told was that it may be caused by the graphic card or the hard drive, but no one seems to know how to fix it. The pc was built manually and it worked fine for 2-3 years. It still works but has this issue from time to time. I can add up here my pc components later if necessary.