Windows 7 - Dvd burner says dic is not empty when it is! please help

Hi, Sorry if this is long.

Basically i have a packard bell computer bought in 2006, havent used for a few years. Wanted to burn a film i down loaded to dvd but kept sayin it was burning but disc would be empty but couldnt reuse disc. Wasted about 30 blank dvds.

I then bought an external dvd writer and have used 3 different brands of blank dvds. Sometimes i can burn films ive downloaded with no problems but half the time it burns halfway through then says disc is not empty when it is. Even though disc was new and empty. Disc says its empty but cant reuse it again.

I have wasted so many dvds and hours trying to figure out whats wrong.

I have also used many different dvd burning softwares which gives me the same problem.
Currently using winavi converter then dvd shrink then nero burn.

Please help. thanks