When your phone gets stuck in a boot loop that's often an indicator the installed Android operating system is corrupted in some way to the point where it won't load up into memory anymore. For a Galaxy S7, it will usually be able to boot up into its Recovery mode (simultaneously holding down the Volume Up, Home, and Power buttons) or its Download mode (simultaneously holding down the Volume Down, Home, and Power buttons) but since your phone apparently isn't able to even boot up into Recovery, that isn't a good sign. It's very unlikely the internal storage chip has failed (that's where everything -- operating system, software, files, etc. -- gets written onto) but possible. Hopefully this is just a software matter, some one-off glitch the screwed up the Android OS.
-- The first thing to try is use Samsung's Smart Switch utility:
This 'might' fix your problem but don't be surprised if it doesn't. Smart Switch is handy as backup/restore utility, fixing serious OS issues not as much. But in any case when you install Smart Switch, it will install the latest Samsung driver on a Windows PC for you.
-- If using Smart Switch does work out well for you, ignore all of the following. In order to reinstall the operating system, you need to go through a process commonly referred to as 'flashing the ROM'. The flashing is the process you perform, the ROM is the software you transfer onto your phone (also referred to as 'firmware'). Go here, select and down the appropriate ROM that matches your S7 model:
It's important to pay special attention to downloading the ROM that exactly matches your model of S7. There are several variations (SM-G970T, SM-G970V, etc.) so pick the appropriate ROM. Do not substitute for one that's close or similar, ROMs are not interchangeable. So pick the one that matches the model I.D., country, and carrier of your phone. When you get to the actual download page, there are instructions on how to do the flashing process. Note you'll need to use the Odin utility, a Windows application, and there's a download link in the instructions. Or go here:
If you don't have access to a Windows PC, try using the Heimdall utility instead:
It's an Open Source equivalent to Odin and available for Linux, Mac, and Windows. Just note it has the same functionality as the Odin utility but it is not an exact duplicate as far as the user interface so you just need to be a little more flexible (i.e. some menus and options have altered naming and/or arranged differently.)
If you have issues using the Odin utility, be sure to go into the Windows Task Manager and kill the Smart Switch process if it's running in the background. Both Smart Switch and Odin are trying to do the same task (remotely access your S7), so they're both using the same system resources of your PC. And be sure to follow the directions using Odin very closely, double-check the option to Re-partition is NOT checked. Flashing a stock ROM onto a S7 'should' leave the user data partition (where all your data is stored) as is. The flashing process only transfers data into the system partitions. If you delete your phone's partition table (either intentionally or inadvertently) that requires your also find and include an appropriate PIT file, and wipes your data.
Flashing a stock ROM is something of a daunting project the first few times you do it, so don't be surprised when things just don't appear to work out initially. Just be patient and follow the written directions (this is now a very well documented occurrence).