My monitor starts flickering after few hours

When I start my pc in the morning, it works fine, but after a few hours, the monitor starts flickering. it continues even if I turn off my pc. If I keep it turned off for an hour, I can use it again for a few hours. But the same problem occurs again. There is no specific time for how long after using it starts flickering. Sometimes it's a couple of hours and sometimes it's 6-7 hours. Also, a couple of times I noticed it started flickering immediately after I opened a game. I don't know if it's coincident or related. My second monitor doesn't flicker, not even when playing games. I am attaching a video to show the flickering. If somebody can help, I will really appreciate it.

Thanks for the response. My second monitor works fine though. I also tried swapping ports but still same issue.

Here is the link you asked.
PSU is Antec Atom 350W