I had exactly this screen problem years ago on my Uniwill L372N1 All-in-one-PC with an integrated Geforce4 420 Go 32M, up to the 5xxx drivers if i remember correctly.
With later drivers (up to 8178) the problem switched to a black screen when trying to start X.
But now with the new 8756 drivers my problems are finally solved, thank god
A hint for you: Try
options nvidia NVreg_SoftEDIDs=0 NVreg_Mobile=1 NVreg_FlatPanelMode=0
in /etc/modprobe.conf, maybe this fixes your problem. Especially playing around with the NVreg_Mobile option is worth a try.
Greetings and good luck
PS: Try starting X with "startx -- -verbose 6 -logverbose 6". Even after a hard reboot i was able to read the logs at /var/log/Xorg.0.log.