well this unit has about made me nuts. they will not stand behind there products>at as a company. out of warrenty>out of luck>throw it in the trash it seems. this beast will try to prepare a disk all day long, then it might tell you invalid disk. now here is the strange part> put a regular old blank cd in it and you can record your tv programs> but it want read any disks at all blank,any body out there got an answer>>>kneelever
Some things you can try:
A good lens cleaning disc
open the drive and clean lens with alcohol amd Q-Tip
take a 2nd DVD drive from your PC plug it into the 5104 and try it out
what media brand are you using? Try Verbatium or Taiyo Yuden.