asking this for my friend,
he is experince this error message while the windows updates done(win2k8r2)
"operating system not found" while reboot the server
try reboot several times but still get the same message,
then, he check the bios for the disc health, seems fine, and after that,
he put the win2k8r2 disc and boot into the window installer screen,
attached with hard disk in bios and windows installer disk selection screen,
he personally suspect the boot sequence wrong, but after reboot, the windows back to normal.
he is worry that the similar issue will keep on repeat after second reboot or windows updates,
he would like to seek advise for this.