Default Phone restarting on its own every 5 sec

Hi ,

This morning my friends phone went derp (9300), it just keeps restarting every 5 sec , so fast i cant even manage to get into download/recovery mode .I can manage to see that "volume up to continue" yellow text in download mode, but it restarts 0.5 sec after that, same with recovery , i can see that stock android icon for 1 sec and then phone restarts.If i dont try to enter recovery/download mode phone just keeps restarting on white Glaxay s3 logo.

Note these

-Phone was never even rooted
-Battery is not problem
-Sdcard/simcard either

Has this ever happened to anyone ? If firmware is the problem is there any way to flash without download/recovery mode , or is there any way to fix it ?

Please , if you know anything that can help write it down