burning Data DVDs - please help

I'm using Nero 6 to burn data dvds and so far none of them have been successful. The burn completes and Nero tells me it was sucessful, but when I attempt to read one of the burned DVDs, windows tells me to insert a disk into the drive. Attempting to explore/open one of the burned DVDs also apparently managed to crash Explorer. I've created a successful data DVD on this machine before, so I know the burner is capable of doing it. One time I chose to finalize the DVD and another time I chose not to. That change didn't affect the final dvd at all, and so far none of them have worked.

I'm using Sony DVD+R disks and I also tried my burned dvds in my other disk drive. both are DVD readers and one is the writer. Please help me figure out what to do; should I try another software? I know what I'm doing, or at least, I thought I did. It's always worked in the past.

edits/notes:
do I need to format the blank dvd before I try to burn to it?

I'm not chosing to make a bootable disk either, so I can't understand why windows or my dvd-rom drives can't read the files on it.

Trying to burn a Nero Image Rom was downright unsuccessful.

I tweaked settings and also reverted to defaults for each individual burn attempt. I also tried using my copy of Nero Express. I even re-installed my copy of Nero 7 Premium to see if it would work. Now I'm using Nero 7 instead of 6 but I still have my old copy of it.

1st attempt was 4+ gigs of audio files
2nd attempt was 4+ gigs of video files
3rd attempt was 3+ gigs of both
4th attempt was 3+ gigs of disk images (legal backups, thank you very much)
5th latest attempt which failed outright was a Nero Burn Rom

Now the process fails outright every time with the error:
Could not complete end of Disk-at-Once



please advise (!!!)