pop out the battery it may be that it's soft bricked if so when it turn back on it will freeze again if it does indeed freeze again pop out the battey one more time and put it back in this time hold the home button volume up and power key until you see blue text appear on the top - left corner of the screen then, it will boot into stock recovery from here press the volume up button to go up and the volume down to go down , select wupe data/factory reset this will wipe the phone,meaning you lose all of your data but your phone should work fine.if this desn't help post back here as it might be hardbricked and that is a difficult but not impossible thing to fix,I have fixed 3 to 4 hardbricked s3's hope this helps,
mitch