I had this problem a long time ago and never found an answer that worked for me...I just had an iPod Touch 4G last week do this after an LCD change, and I fixed it. I had another one do it today, and was able to confirm a fix
Here is what I did:
1)while PLUGGED INTO COMPUTER, hit power/sleep to blacken screen ('''if it is already black, toggle through white screen and then back to black''')
2)press home button in and hold, immediately press in power/sleep and hold
3)hold until Apple logo appears, release