If the screen is broken it needs to be replaced. You can order a replacement part online through ebay, amazon etc. There are numerous tutorial videos available on youtube that guide through the replacement process. Replacement cost ranges from $20-80 depending on the supplier, labor costs and shipping.

Try a different SIM card. If so and the problem still occurs, you might need to get a new antenna flex cable for your phone.

Make sure that the lock-switch connector is on fully, and that it’s not broken or faulty. Replace the phone battery. Also look for issues with the IC as fluid contact can damage the internal components of these micro computer devices.