Nvidia BFG 7900gt DVI problem - No Signal

Hi everybody.
I have a custom pc with an Abit An8 fatality mobo, the geforce bfg
7900gt and a acer 17'' flat panel monitor.
Everythings works fine until a month ago, when suddendly after boot a
have "No-SIGNAL" on my monitor. I wait until boot was made (some
minutes), but nothings happens.
I have put a dvi-vga adapter (the bfg card comes only with two dvi) and
it works!
Now my question is:
where is the problem?
I have tried to change the dvi cable, but i have always "no-signal".
Now i had to try the cable with another dvi card and the monitor with
anoter cable/card.

Is it possible that is a geforce problem?
Is it possible that in the vga card the dvi output is broken but the
vga works (they stay on the same port!).

Have someone some ideas?

Driver are the last from Nvidia (84.21)

Find a way to swap parts into a working system, and
determine which is the bad part. If it is the 7900, it has
a lifetime warranty. Ship it to BFG for replacement. Also,
Acer is a really low quality monitor. That should be easy
to check out. I doubt it is the cable. I remember that the
7900 from BFG shipped in quantity so fast that there
wasn't time to check the cards. Many of them shipped
DOA with parts falling off in the box.

johns