Ipod lock

Hello,
i was playing with my ipod until i got it locked by mistake ,, and for long time i've been trying to remove the lock but the ipod doest work if i connect it to the computer it opens and start charging ,, but when i disconnect it doesnt work ,, i wana knw how to make it work ? i've been trying for a long time but it's not working....
i would apperciate if u help me in it plzz
thnxx aloot