I’ve run into this interesting problem while fixing a laptop recently. It has dual boot with Debian and Windows 8.1 installed. When grub launches, neither option (Debian or Windows) boots successfully, but the computer is restarted.
Another thing I noticed is that the main screen for grub shows with poor color quality (16 bits). My best guess is that the grub configuration file must be messed up. Other suggestions or ideas will be more than welcome.