How can I fix Hitachi DZ-MV3000E?

Last used a DV-R disc cannot remember if I finalised it or not. But tried a DV-RW disc in and says "Cannot read disc" "Check dirt/crack/both sides contrary/inserted correctly. checked all these and still problem. Think this could stem from the initial DV-R disc so tried to finalise it,unable not on menu (Manual says if not on menu then its finalised). So checked on disc navigation menu and if finalised should say "F" does`nt says "R" indicating that its not finalised. Think this could be the problem. Can anyone help please. Thankyou