Cracked screen replacement problem

I dropped my Galaxy Tab 4 about 6 inches onto the ceramic tile floor, cracking the screen. So I ordered a new digitizer and very carefully removed the cracked one and installed the new screen. Everything went smoothly.

I got it all put back together and turned it on. Now the touch response is intermittent and the two touch buttons that flank the main button do not work.

What's the problem and what is it I might have done to screw this up?