Mine had a loose connection at the ODBII connector. The wires appeared to be still connected and covered by heatshrink, but the they had snapped underneath... so i pulled them off and resoldered them.
The throttle should still work as you describe now, but also the screen should illuminate when just plugged into the ODBII and not the throttle... how about getting a 12v source from somewhere (8AA batteries, an electric drill etc) and tapping into the power wires... thats where i'd start...