Γεια σου για δοκίμασε αυτό.....:O:O
Take out the battery, then press and hold the ON button for 7-10 seconds (the longer the better). Reinsert the battery, then press ON button to start it. This is a soft reset, and wipes the temporary memory and empties all remaining power in the circuits. This helps on many phones and even laptops that won't start properly or show anything on screen.
If this does not work, try the next step. Again, do as above. But after inserting the battery, do not turn the phone on, but press and hold the ON button and the HOME button at the same time for 7-10 seconds. This is a hard reset, and works best if done after a soft reset. Just be sure the battery has at least some juice in it and isn't empty. If possible, try with another battery if this does not work.