So it sounds like something happened that corrupted the Android operating system on your phone bad enough that it just won't boot up normally again. So try holding down the Power button for several seconds, as long as it takes to force the phone to shut itself off.
Now try one of these two to see if your phone is indeed 'dead' or it's just the OS that's corrupted.
Recovery Mode - simultaneously hold down the Volume Up, the Home, and the Power buttons. It's not the most elegant arrangement for your fingers and if you haven't done this before it takes a little getting used to but you do need to firmly hold down all three at the same time during a cold start. Once in your S7 is running in its Recovery mode it will be a text-only user interface. Recovery mode is only to be used for fundamental maintenance tasks.
Download Mode -- simultaneously hold down the Volume Down, the Home, and the Power buttons. Download mode is for when you want to flash software/firmware.
Keep in mind these more or less independent of the Android OS, they're at a lower level closer to the hardware of your phone itself. If you can boot up into one or both that at least means your phone is still functional at some level, it's just the OS that's apparently messed up.
If you've used Samsung's Smart Switch utility before and have your S7 registered, try using Smart Switch to fix the OS.
https://www.samsung.com/us/smart-switch/
This probably won't work out but worth trying.
You can try and manually flash a new firmware (a.k.a ROM) to see if that restores your phone back into working condition. Flashing the ROM is essentially the same as using a Restore disc/media to reload the operating system on a PC. The flashing process overwrites a clean, new OS, replacing the installed one. Go here and download the appropriate ROM for your model of S7:
https://www.sammobile.com/firmwares/search/galaxy s7/
Be sure to use a ROM that matches your specific model, they are not interchangeable. Pick the one that matches your model I.D., country, and carrier. When you select the ROM you need, the download page has instructions on the flashing the process. Don't experiment with the Odin utility, if you follow the directions there's a good chance that your files and documents will still be there after flashing the ROM -- The internal storage media in your S7 is divided into several partitions, most are used for the operating system and one is dedicated as the user's data storage partition. It's the OS partitions that get overwritten during the flashing process, the data partition should be left as is. (well, as long as you follow the directions).
But all this depends on the state of the phone. If you can't even get into Download mode for example, that also indicates you might have a more serious hardware problem. In that case it might be better to just take your phone to a local service shop to have it looked into (well, allowing for all the social distancing issues we're going through).
