I need a replacement motor on a KitchenAid Professional HD Stand Mixer (Model KG25H7XSL).

The Service Manual for this model (yes, it covers the 5 qt. model as well) can be found at: http://ep.yimg.com/ty/cdn/mendingshed/kitchenaid6qtservicemanual.pdf

The motor for sure. The speed selector too.

Remove the top cover, screws are under the metal trim band with the writing on it. Get a multi meter and follow the power. Where the power stops is a good place to start looking. I think the electric internals consist of a PCB complete and a motor complete. If the motor has a circuit and both field windings are even resistance then you are probably looking at a pcb replacement unless you are an electronics whizz. There may also be an interference suppressor across the mains power supply in some countries, unlikely that will stop it though. Certainly look for any unplugged or broken connections inside from mains cable to pcb.

Check different outlet. Make sure the outlet isn't at fault.

Look at the bottom of the bowl to see if it's dented first. Replacing the bowl is the only fix.

If they are metal shavings you have a bad gear in the motor head. needs tear down and new gears. YouTube video will show you how to do it easier than I can write it. If you don't find it let me know I can point you to it or walk you through it. Going to cost around 70 dollars

It shouldn't do that, and I really doubt there's anything you can do about it other than to have the defective part replaced. It sounds to me as though there's a problem with the control mechanism. If the machine is still under warranty, contact Kitchenaid to see about getting it repaired or replaced. If not, get the name of a local shop that repairs Kitchenaid mixers -- from your description of the problem, the mixer is nearly unless in its current state.

How comfortable are you with electrical parts? With the mixer UNPLUGGED and the switch ON measure resistance between the (flat) plug pins. If it's infinite (no meter movement) which is to be expected, there is an open circuit. The switch could be open or the wire to the switch could be disconnected (improbable) or the motor could be burned out and open (not very probable).

Maybe you could take the switch to a shop and have it tested.

This is not really a solution, just step 1.

Check to see if the contact points on the control board are working. Adjust the screws at the top of the control board until the contacts make contact. That should fix your problem.

remove the top etc. and replace the gear