Drive letter randomly changed, OS wont boot

Sadly I had to join here due to a problem with my 2 week old win 7 64 install.

I'm not sure what the trigger was but my C drive where my os is installed apparently took the drive letter of an external drive that I use for backup. It is now the X drive and I cannot boot. I do get the repair screen but cannot repair as there is no operating system to choose. Booting from windows disk makes no difference here.

My bios (uefi) can see the disk, I can also see it from the command prompt, Im at a loss what to do, any help is appreciated.

I believe this happened after an automatic windows update.

By the way, this is a newly built computer, clean install on a new hdd. Running fine for last 2 weeks.

Boot sequence is my WD hdd, then optical drive.

The external drive is disconnected.

After digging deeper, my assumption about C drive taking the X letter was wrong, coincidental I guess. Apparently X is some setup default (?). There are only some windows sys files on the mysterious X partition. The C partition is nowhere to be found.

When I boot I get the msg that windows failed to start and have the option to launch startup repair or start windows normally, either will result in the system recovery screeen, which ultimately doesnt work. There is no OS to select to repair. If I choose use recovery tools and try startup repair it reports: startup repair cannot repair this computer automatically, with a problem event name: StartupRepairOffline

I can go to command prompt and tried discpart list disc which reports no fixed discs.

My bios does recognize the WD hdd however.

X is WinRE.

If you're using EFI then the BIOS Boot Order should have a listing named EFI boot disk and it should be set first to boot.

If not you're not installed in EFI so try these steps for Troubleshooting Windows 7 Failure to Boot - Windows 7 Forums