cell phone touch screen

I've bought a load of touch sreens cell phones to make som money from an auction, the software on the touch screen shows a blank but the sound still works, i need a simple lesson on how to fix this problem to save money, anyone out there who knows please help

Considering we have no idea of any kind what you're talking about... not not really...
Some real information might be in order.

screen broken? Ribbon cable damaged or no installed correctly? need more info.. What is it attached to?