GRUB2: black screen when booting Windows

I know this might be a duplicate, but I've read a lot of threads about this and none pointed me to the solution.

When loading GRUB2 I have a black screen (with static white cursor on the upper left) which goes away as soon as the Ubuntu login page comes up, but stays there forever if I boot Windows (even though I can hear the 'login sounds').

I have a dual boot system with Ubuntu 14.04 and Windows 7 (both 64-bit) and I have a NVIDIA VGA. The Windows installation used to work just fine, with the VGA doing its job. My monitor was plugged on the motherboard when I fresh installed 'trusty tahr' (I have a integrated intel graphics CPU) and after that I immediately installed the video card drivers from the official repo (nvidia-331 I believe). Their installation was successful (at least from what I see from the 'Nvidia X serve settings' tool). After that, if I plug the monitor on the video card, grub goes on the black screen, but I can anyway boot Ubuntu and when the login page comes up the video output is normal. The same cannot be told when Windows boot.

I tried many suggested fixes: nouveau.modeset=0, nvidia.modeset=0, nomodeset options in the /etc/default/grub file and I also tried blacklisting the corresponding kernel modules adding a .conf file in /etc/modprobe.d. None of that solved my problem.

I insist that this must be a grub video problem, since if I plug my monitor on the mother board I can boot successfully both Ubuntu and Windows and also the boot-repair tool for Ubuntu doesn't find anything significant (see http://paste.ubuntu.com/8552162/).

I'm currently out of ideas, has anyone any suggestion? It would be much appreciated!

Lorenzo

When grub start windows, everything shall go on win7 hands... so I think the problem start before. It's a graphical problem, so I let grub work in no grafical mode at all:

sudo gedit /etc/default/grub

# Uncomment to disable graphical terminal (grub-pc only)
GRUB_TERMINAL=console

sudo update-grub

if don't work, I shall look bios setting looking to uncorrected configuration on pci or graphics CPU capability.