IPhone vibrate switch is broken

This problem was caused by the light through the 2 holes of the glass.You can cut a black tape with 2 holes, and cover it on the sensor flex cable. It can resolve your iPhone 4 Proximity Sensor Not Working problem perfectly.
iPhone 4 Proximity Sensor Not Working

The screen or battery may have malfunctioned. I'd say take it back into the store and if it's under warranty they should fix it for free. If it's not under warranty, ask them to find out what's wrong with it and it may be a cheap problem to fix.

Ah, this is a common problem after dropping an iphone.
If you had your iphone for less then a year then you could try taking it back to the apple store and say the screen has stopped working and they should give you a new one under warranty. I wouldnt mention you dropped it tho ;).
If you have had your phone for longer then a year or apple wont give you a new one then you should seek help from a repair company such as the one below. Shouldnt be too expensive to fix
http://www.iphonerepairservice.co.uk/

you can still push it up or down with a thin stick. we actually have the same situation and I don't want to take it to someone for repairs coz it's gonna cost me around $50..

Take it to the apple store. Even if it is not under warranty the guys at the genius bar should be able to fix it.