i don't even know if this problem has anything to do with GRUB or Ubuntu. It could be just a hardware problem.
my problem started after i installed my new graphics card (Radeon HD7970). Everything worked flawlessly with my old Nvidia GTX470 card.
I have a dual boot system (Ubuntu and Windows 8). If i start Windows from the GRUB boot loader it switches to a blank screen after a few seconds. I think that the system is still booting up because i hear the hard drives and the keyboard also flashes shortly. The screen also doesn't show "no signal". It's just blank. The same thing happens with Ubuntu. But not everytime. Sometimes it boots just fine. So i basically have to reset my Computer again and again until it works.
My processor is an Intel 3770K with integrated GPU. I think that maybe the Computer uses the wrong graphics output when booting from grub. Maybe it switches to the iGPU.
I can't disable the iGPU. There is no option in the BIOS. My board is an (Asrock Z77 PRO3)
If i reinstall the Windows boot loader, Windows boots fine and without problems. I only get this problem when launching any of the systems from GRUB.