Is it just NERO 7 that cant write? have you tried another tool (or even native burn capability in Win 7 (and vista?)).
Just to make sure its not Nero gone bad (Nero 7 is VERY old).
It is probably the burn laser gone bad.. but worth checking it not a software first. Th0 egood news is that DVD writers are dead cheap if you do end up needing to replace.
i m using xp and yes i have tried other softwares too.