Studio 1555, when burning DVD's, msg "not a writing drive"

Studio 1555, Win7 x64 bit.

Reads CD's & DVD, writes CD's, but I get the message when I try to burn DVD's.

Does not matter what program I try, built in Win7 or stand alone (I use Deepburner).

I've NEVER used or installed any other burning software, I've looked for the "upper & lower filters",

but there are none.  Dell shipped me a new DVD (even was a different brand).  After I installed

it, I was able to write a DVD, but the next day, after a reboot, the "not a writing drive" message

comes back.

Any ideas?

Tnx