My hand hurt real bad after I done a song on hard.
What was wrong with it?
And what is the worse that could happen to my hand if I play non-stop, on hard?

It's not the game. Your probably trying too hard, your playing wrong, or you have small hands. Either those, or your not ready for Hard.

your hand will probably fall off in about a week or so. activision luckily sells replacements for only about $20

but really, its just an unfamiliar motion-- you'll get used to it over time.

It only done it when I played 3 hard songs, in-a-row.

Your hand isn't used to playing Hard mode. Mine did the same whenver I played Medium mode and Hard mode.

quote Scorcher

your hand will probably fall off in about a week or so. activision luckily sells replacements for only about $20

lmao XD

Just muscle cramps in your hands. Your hands and fingers have hundreds of tiny muscles and tendons that aren't accustomed to the motions. Unless you have some sort of disorder it won't hurt anything permanently.

Your hand will get used to it and will stop hurting