I first installed Windows 7 and then Ubuntu 17.10 along side the windows. Ubuntu can boot without issue. But if I select Windows7 from the GRUB bootloader, something strange happens.
40% chance the screen turns magenta (same color as GRUB background) and freezes
40% chance the screen turns magenta but the Windows 7 startup sound can be heard
20% chance it can actually boot into Windows 7 without issues