There are issues with the iPhone when the 3G screen goes blank or black. Press sleep/wake twice consecutively, which locks the phone, and then try unlocking it. This problem may also be due to obstruction of the proximity sensor because of the case or an errant hand. Not all iPhone users have these interference factors; even after resetting several times, working to restore build 7 is of no use. Lastly, a new firmware may help solve the issue. To try a workaround solution, this issue can be resolved by turning off the Password Lock (PIN) function in Settings. Issues like this are common in iPhone telephony.
It may happen that your iPhone screen goes blank.
Before assuming the worst, try the following steps to try to rectify the problem:
- First, check that it still vibrates on an incoming call or SMS
- If you can't turn it off/on, connect the phone to your PC and see if it is detected and if it starts to synchronize
- In this case, connect your iPhone to your PC and try to reset it using the method described in this tip.