Why won't it turn back on. Help please...

The question may be what's expected battery life before it wears out? A worn out battery may be the reason for your watch not powering up. One way to tell if the watch is faulty or a dead battery would be opening it and noting battery voltage, usually printed on the battery. A substitute battery of any size with correct voltage can be temporarily wired in after removal of the main battery. With correct connections, turn on your watch. If it turns on and runs, replace the battery. If this temporary battery doesn't turn on the watch, it's faulty and non repairable.