appletv

A continuously flashing status light indicates a failure to start up properly.

If a restart of the box doesn’t improve the situation, then the system software may need to be reinstalled. If you can’t access the on-device menus for a restore, then the restore has to be done externally, through a computer. Unfortunately, for the 4K model, users can’t do this themselves. Contact Apple to have it serviced. Restore your Apple TV - Apple Support

You can, unplug it from it's power source for a few minutes and then plug it back in and retest.

If the flashing continues, please first Identify your Apple TV model and then follow the directions in Apple TV Reset or restore your Apple TV to its factory settings for the model Apple TV you own.

Please click the Identify your Apple TV model link in my first post. That will help you find the model of Apple TV you own.

Do you have any idea how much they charge to do that

I shouldn’t speak for Apple; they would tell you that. It should be one of your questions when contacting them (e.g. “If there are costs, then let me know your price quote”). It may not be the same in every country or region, and a restore of the software may not be the only issue. (I’ve heard stories ranging from “free” to “buy a new one”.) Be sure to ask for a “restore”, not a “repair”. Repair is a differently priced service (with fixed costs in most countries).

All this assuming the A1842 4K (2017) model, which doesn’t have a USB port to do an external restore yourself.

Likely nothing however we cannot be sure. I would recommend that you contact your local AASP and ask.