Wipe the device using JL_CMDER or BBSAK. See BlackBerry FAQ - BlackBerryFAQ
. The wipe will leave you with a 507 error (no device software) which you probably won't see anyway with the display fault. I guess if you do see the 507 error that will be a good sign.
After you wipe the device, reinstall the OS either from your carrier, or install the latest official release following the directions in the "latest OS" stick thread for the 9700.
Good luck. Fingers crossed. (If it is a hardware problem, I don't know what is involved to fix.)