M17x won't power on but keyboard lights work

use the softare diagnostic coming with the computer or get support via ONLINE chat.
However you must restart the computer HOLD the keys CTRL+f2 or f11 or f12 depend of your model, and go to restore to the factory defaulty.
God bless you

unplug, take out battery then hold power button for 30 seconds then plug back in and turn on
if the3 laptap gos on without the battery you need a new battery

First of all, did they worked before?
If yes, then it means your Alienware maybe went into a power saving mode because the adapter you're using doesn't provide enough energy.
If the lights didn't worked before, then you should install all the necessary drivers and the Alienware OSD Application and Alienware Command Center.
If you have all the applications and drivers installed, then you should configure the lights in the Alienware Command Center.
Here are the official links for drivers and resources:
Alienware M17X Drivers:
http://www.dell.com/support/troubleshooting/us/en/19/Product/alienware-m17x
or
Alienware M17X R2
http://www.dell.com/support/troubleshooting/us/en/19/Product/alienware-m17x-r2

To do a power reset, unplug your laptop, remove the battery and hold the power switch down for 30 seconds.

otherwise it may be problem with your screen back light...

Just because they hit the tower should not have hurt anything.

But, you should turn it off, pull the power plug, then hit the power button, then again and make sure the lights don't turn on or flash.

This make's sure that all the power is gone from the motherboard.

Before you touch the inside, make sure you touch metal, so you don't static shock the motherboard.

Now open the the side up. I would remove the two power connectors, one should be a 20-24 pin and another 4 pin.

Reset them to make sure they didn't come lose.

Check the HDD, hard drive plugs, fan plugs, the CPU fan plug.

Then check the monitor connection, and any on the back.

Try the monitor on another PC, or a monitor from another PC on this PC.

A hard shock to the power supply unit (PSU ) can kill it, it can still turn on the lights but not have the voltage to run it.

If you do all this and are safe and careful checking inside and out, then you might have to take it to someone who can test it.

You can also download the manual so you know what it looks like inside the PC and what the motherboard looks like and how you would set it up when new.

Good luck.

Have you done any updates to the BIOS?

So there is not so much as a BIOS message on screen? Any beeps?
If there is no life at all, you have a CPU/motherboard failure. This may be direct or indirect (e.g. no power to MoBo). Check your connections.
Otherwise, your boot device may not be operating. This is usually a dead or disconnected HDD. Check that it is plugged in. Does it get warm? Can you feel any vibrations from it? It should spin even if your cpu is dead but MoBo is alive.

Make sure the VGA cable is properly inserted to your pc and monitor

Try to run it with only one stick of memory in at a time. If the memory doesn't work the computer won't even go into the POST. It only takes one failed stick to stop a computer.

First up, don't buy a Dell again unless you like old **** with horrible support.

On Topic

- Did you pull out the keyboard and try another USB port (if it is an USB keyboard), or try another keyboard.
- If that doesn't work try clearing the CMOS (remove power plug, power on (to empty capasitors), either remove the CMOS battery and power on, or find a jumper to reset the CMOS. (since this is a Dell a that might not exist but check the manual).