OK, so it looks like my original post never went through, so I guess I’ll just try again…

I have an Asus X401A laptop that my kids use for school work. Recently had to replace the screen on it because one of the kids cracked it. Bought a replacement via Newegg, and the installation went without any issues. System booted normally and worked fine afterwards.
I decided to then take the opportunity to install a new keyboard. I had purchased a replacement on Ebay last year and just never got around to it.
Keyboard replacement went well, but now the unit will not boot. On power up, the power LED lights up, and the hard drive LED comes on for a few seconds, then immediately goes out. No other lights and no display.
I tried putting the original hard drive back in. (It was replaced for a larger capacity drive last year.) No good.
I tried all the usual tricks you find on Google: Holding the power button down for 20-30 seconds with the battery removed, powering it up without the battery and just the AC adapter, holding down F5 while powering up, etc. Nothing helps.
I figured I must have fried the motherboard, because I thought a piece of the metal backing on the keyboard must have touched it due to the clear plastic covering being slightly out of place. Bought a new motherboard from a local shop. Same result. No screen, no lights, except for the power LED. I even tried powering it up without the keyboard connected, to no avail.
Anyone got any more ideas?