If you plug in the AJA U-tap device along with the HDMI source and only see color bars instead of a video image, this means the AJA U-Tab isn't receiving a video signal. There are usually two easy solutions to this problem.
1) Make sure all HDMI or SDI cables are securely plugged in.
2) If you are using Avid Media Composer, visit 'Tools' then click 'Output' or 'Output Tool' in the menu. Make sure that output is set to 'True P' which means true progressive.