Remove the battery for an hour or so then re-insert and let charge (don't try to power on). After an hour of charging try to power on and see what happens. If it doesn't, then I suspect the battery may be bad and needs to be replaced. You can find a replacement online for a reasonable price. However, you'll be without a phone if a backup is not available.My S4 mini's battery went down and when I started charging it nothing happened. I took battery off and put it back still nothing. What should I do?