The X:\ is just the drive letter assigned to the RAM storage. When you boot into Windows PE, it loads the OS into memory and gives it the X drive letter.
I've seen this error happen when booting the PE environment from a USB3 port, or a port that for some reason Windows PE doesn't like. Try using another USB port or if possible, a bootable DVD of the Windows disc.
If that doesn't work, try running the bcdedit /enum all command. That should list the OS and the bootmgr (if it exists). If you see your Windows install, run bootrec /fixmbr and then bootrec /fixboot. If they complete ok, then run bootrec /rebuildbcd.
If the above fails then it could be that you are lacking either the 100mb boot partition on the main disk or have another boot issue. For that I'd run this command bcdboot.exe C:\Windows C:.
Definitely try the alternate USB port then DVD disc first though. You'd be amazed how often the recovery environment fails to fix problems when it boots from USB!