Check the power cord or try plugging the router into an uninterruptable power supply which will maintain power for brief outages.

Good luck

If it’s going dark/black randomly, someone may be accessing your computer remotely and darkening the screen so that you don’t see what they’re up to. Google RAT or random access trojan.

When in doubt, factory reset it.

Does it happen only when *your PC is connected to the Internet? If so, you may have installed a RAT that has granted a hacker remote access to your PC.

The next time it happens, disconnect from the Internet and see it the problems persists.