Reading through your description it sounds like your S7 is booting up into its Download Mode, something that you can do if your restart your phone by simultaneously holding down the Volume Down, the Home, and the Power buttons. But if your phone is starting up all the time by itself that way, that indicates the installed Android operating system has become corrupted or deleted -- the issue being if there's no functioning operating system that's just the your S7 will do. What worries me is your reference to doing a reset while starting your phone up holding down the Volume Up, the Home, and the Power buttons. That takes you into your phone's Recovery Mode, which is normally used only for lower-level maintenance tasks, including doing a Factory Reset. This should affect the operating system though even if you did, but is there a reason as to why you booted up into Recovery Mode and do you recall what you did do?
Anyway, do you keep your phone inside a case? If yes, try restarting your phone while it's not in the case in the event it just became inadvertently shifted out of place causing some of those buttons to be pressed down. It it appears to be stuck in Download Mode, hold down just the Power button (for several seconds) until that forces your phone to power down, and then try to just start up normally and see what happens. Hopefully it will just boot up like it should, but if it boots up into Download Mode again let us know.
