I dropped my 18volt dewalt about 2feet and now it won't work at all, what would cause this from a small shock like this?

Only if it is an 18volt motor.

Or compare before with 18Volt Milwaukee FUEL impact wrench on Li Ion Battery [ try before you buy ] its having very much power.
But if you have work the whole day job the best choise for long lasting air tools

Where is serial number on Dewalt cordless dcd785

You can actually send it back to Dewalt and if it is still under warranty they will fix it or if not under warranty they will fix it for 40 bucks

Please visit a qualified technician. Because it's also my personal experienced with hammer drill that inside a small ball bearing with tiny spring as a tosser for shifting always been stocked up by sticky or hardening grease which you need to loosen. If not kindly check it up for something that is blocking the shift. Thanks for asking.

the chuck is held to the drill by a small allen head screw that is down in the base of the chuck -- it is a reverse thread.
after the screw is removed - the chuck should pull off.

c...

Yes. Dewalt says the 18volt XRP battery is compatible with all Dewalt 18volt tools

Have a great day.

there is a screw inside the chuck inline with it, I believe it has a reverse thread so turn it counter clockwise to remove

http://www.sears.com/shc/s/p_10153_12605_00981808000P?vName=Tools&cName=PowerToolAccessories&sName=Batteries%20and%20Chargers&psid=FROOGLE01&sid=IDx20070921x00003a

the newer type of battery had an electronic inside only. older style battery had sensor only.