All that you need is set your disk to LBA mode in BIOS. Dont leave
there AUTO. Thats all. Linux read BIOS access mode wrong and grub
setup something wrong on MBR - its why windows boot manager cant be
find in MBR and windows cannt start.
Attention. Please, check what access mode you realy normal use to
access disk. Changing access mode from Large to LBA for example can
lead to lose data from your disk!