iPhone 4S Glass is Shattered
Broken Rear Panel
Apple did not grace the rear panel of the iPhone 4S with the same high-strength glass as the front, so fractures are much easier to come by on the backside. If you read panel is smashed you must replace it with a new one.
Broken Front Panel
In most cases the iPhone will still work, just looks like an eye sore. The LCD/Digitizer are fused together and need to be replaced as one part.
iPhone is frozen or unresponsive
Sometimes all it takes is a restart for the iPhone to become responsive again. To restart your iPhone when it is unresponsive, press and hold the sleep/wake and home buttons until the Apple logo appears. This should take approximately 10 seconds.
Very Low Battery
It is possible for an iPhone to become unresponsive if the battery drops to an extremely low level. Plug the iPhone into your computer or wall charger and allow it to charge for at least 20 minutes before using it again.
iPhone 4S will not charge
Bad Cable Connection
Check the USB cable for damage and dirt, especially at the ends. Then try using the wall charger, as this will provide greater power than the computer/USB.
Obstructed/bad dock connector
Inspect the 30-pin dock connector at the bottom of the iPhone for dirt, lint, and damaged pins. Clean out the dock connector very carefully with a tooth pick or soft toothbrush. If the dock connector is broken, you will have to replace it.
Plug your iPhone into your computer or wall adapter to charge. If it does not charge when connected to either of these, you probably have a dead battery. The battery will need to be replaced with a new one.
It is possible that it appears nothing is happening because the display is bad. If the iPhone sounds like it is working properly but nothing is visible, it is possible the display is bad and must be replaced. Unfortunately, the LCD and glass panel are fused together, and must be replaced as one unit.
Bad logic board
If nothing else works, your logic board is probably bad and needs to be replaced.
Obstructed/bad dock connector
Check the 30-pin dock connector at the bottom of the iPhone for dirt, lint, and damaged pins. Clean out the dock connector very carefully with a tooth pick or soft toothbrush. High concentration isopropyl alcohol (at least 90%) and a cotton swab should be used to clean any debris that does not come off with a tooth pick or soft toothbrush. If the dock connector is broken, you will have to replace it.
Dirty or corroded logic board connections
After an iPhone has been submerged in a liquid, there may be some corrosion or debris on the logic board connections that cause this error message. Remove the logic board and clean all of the contacts with a soft cotton swab and high concentration isopropyl alcohol (at least 90%).
Dirty antenna grounds
If your iPhone has been disassembled before, it's possible that finger oils were left on the grounding locations for the Wi-Fi or Bluetooth antennas. These oils will cause grounding issues for the antennas, which could lead to a weak signal or no connectivity at all. Be sure to clean all grounding points with an electronics cleaning solution before reassembling your iPhone to prevent grounding issues.
It's unlikely your headphones or speakers are bad, but it's worthwhile to eliminate these as the source of your problem at the beginning. Try your iPhone with another set of headphones or speakers just to make sure that the problem is with the iPhone.
Bad audio jack
The most likely cause of audio output problems on iPhone 4S is a bad audio-out jack. If you have determined that the problem does not lie in your external speakers, you should replace the headphone jack.
It isn't often that Apple gives specific directions about how to fix your problem! Restoring the iPhone 4S will erase everything on it, so make sure everything on the iPhone 4S is stored elsewhere prior to restoring. To restore, connect your iPhone 4S to a computer with iTunes installed. Click "Restore" on the iPhone 4S summary page (click on your iPhone icon on the left menu to find this page). Follow the directions to restore. If your iPhone 4S displays the text "Please wait. Very Low Battery," leave it plugged in. This charges the iPhone 4S enough to be able to restore. If the iPhone 4S hangs on this screen for long periods of time, you may need a new battery.
Force restore mode
If your iPhone 4S is hanging with an Apple logo, or exhibiting some other software problem that prevents iTunes from recognizing it, you can force it into recovery/restore mode and then use iTunes to restore the software.
If the device is powered off, plug one end of your USB cable into the iPhone 4S and leave the other end disconnected. Press down on the Home button, and keep holding it down while you plug the USB cable into your computer. After 5-10 seconds, you should see a "Please Connect to iTunes" image on the iPhone 4S, and iTunes should prompt you to restore the software; follow the prompts and the instructions given above.
If the device is powered on, hold down both the power and home buttons until the device reboots and displays the "Connect to iTunes" image (generally, 5-15 seconds).