My galaxy s3 mini will not restart A few days ago my s3 mini turned itself off and it won't restart. I have charged and changed batteries but nothing happens. I have tried several times but the screen just does not come on
Regarding the basic problem - if the phone isn't showing the battery graphic when you connect the charger, that's a bad sign. You could try booting into Recovery mode or Download mode just to see what happens :


you use Recovery mode to clear the system cache and to Factory Reset
you use Download (aka Odin) mode (showing the Android guy) to load/reload firmware
the key sequences to enter both modes are very similar, and they are timing dependent so it may take a few tries to get it working
-- Recovery = Volume Up + Home + Power
-- Download = Volume Down + Home + Power
for either, you start with the phone completely off
press and hold the required keys simultaneously, and release them all when you see the swirling logo (not the static white text)


Try Recovery mode first (use the Volume rockers to navigate; use the Power button to select) and if it boots into this mode just clear the cache and then restart. If the phone doesn't boot normally then try Download mode.

If the phone doesn't respond to either of those methods it's time to take it in to your place of purchase or your local carrier store.

Source : Android Central

Hope this helps !