often you have an issue with the power supply or backlight inverter...but sometimes the issue lies within the analog to digital driver board for the panel.
http://www.ebay.ca/itm/262096595319?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITI have bought a couple of these and used them to replace the A/D boards in a few ELO touch panel monitors used in older touchtunes jukeboxes.
it requires a bit of knowhow to wire up, but once you know what you need, it's easy peasy.