My Canon Powershot SD400 won't turn on and lense won't go back in

Unfortunately the lens assemblies in these compact digital cameras are quite delicate. The drop probably knocked the barrels of the lens out of alignment preventing it from moving. You can try to GENTLY twist the lens back and forth, you may be able to click it back into alignment allowing it to function normally. If the gentle manipulation fails to fix the problem you will need to get the camera serviced by a professional. There are quality repair services on the web who will work on your camera. David Millier Advance Camera Repair