First, remove the battery and check the SIM. Make sure that the SIM door is locked and not loose. Once the SIM door is loose or unlocked, your HTC will shut down automatically after entering the code.
If same problem occur, then you need to send the phone to the manufacturer for repair. There are damaged components inside that needs to be replaced.
If the phone is under the warranty period, have them repair it for free.
Answers & Comments
First, remove the battery and check the SIM. Make sure that the SIM door is locked and not loose. Once the SIM door is loose or unlocked, your HTC will shut down automatically after entering the code.
If same problem occur, then you need to send the phone to the manufacturer for repair. There are damaged components inside that needs to be replaced.
If the phone is under the warranty period, have them repair it for free.
Thank you and good luck!