My guess is defects in the LCD display itself. The display on the stock radio in my 90 before I ripped it out was the same way, I assumed the radio was trashed too since no sound, turned out to be a shot stock amplifier.
There is probably somewhere you can get the radio reconditioned if you wish to keep your car stock, otherwise it's pretty easy to upgrade to a nice DIN sized CD player etc..
------------------
Frank W 90 5.0 LX Notch MAC 2.5"cat bk FMS alu ds, MSD coil, MAC shifter 2.73 gears
user site
My 90 Notch and 88 2.3 Notch(88 for sale)
74 Chevy Laguna Type S-3 305 now 454 soon
My web site