After I upgraded my i3GS from 3.1.3 to iOS4 yesterday morning around 7am, everything working fine till yesterday midnight. I tried to sync my i3GS with iTunes. Syncing successful except for back up. I can't back up my i3GS. Error said iTunes could not back up iPhone because iPhone disconnected, pop up and I little panicked. Then i tried to restore back my i3GS but the the restore finished it halfway and error 29 pop up. My i3GS stuck at recovery mode. Then i do some research and finally I kicked out from recovery mode and also managed to restore back my i3GS but something bad happened. My i3GS keeps restarting after a few minutes especially when it is on charging or when I using it.

Is it iOS4 bug or my i3GS's hardware faulty? Before this my i3GS had been water damaged and recover from it. Only headphone jack defect. Is it possible to change the water damage indicator to normal and go claim warranty or iPhone repair shop could repair it if i3GS warranty has ended up?