I have a Dell 15 XPS 9550 with suspected liquid damage. When turning on it illuminates the Power button LED for 20 seconds and then goes off and the front two LEDs both flash white once. Then nothing.
The screen never comes on. The fans never spin up. There are no beeps.
I have removed the battery and the CMOS battery. I've stripped it right down cleaned it with Isopropyl Alcohol and put it back together - same result. Makes no difference if battery is connected or not.
Apologies that your computer may have been damaged. It looks like you've gone through all the steps to bring it back to life. I had a similar issue not long ago and I placed mine in a large bag filled with silica gel packs for a week before applying the power to it. Mine came back, but that doen't always happen.
lf you purchased the Accidental Damage insurance when you bought it, you may be able to get it repaired under the warranty coverage. If not, then you may have to refer to our Out of Warranty Service Department for an estimate of the costs to repair it. Or, you can take it to a local computer repair shop. http://dell.to/2xtrR3q