From working system HDD to External, but not back again.

[bushido]

So i recently needed to take one of my hard drive out of my desktop, because of a power outage, I used my system HDD, as it had most of my movies. I used it as a external HDD, but as soon as i put it back in and tried to boot, it got to DMI Pool checking, and no further. Then when i isolated the drive and tried to boot solely with it, it got a DISK BOOT FAILURE. The harddrive still works, as i booted it as an external, but it failed to repair itself. Best case scenario is that its something simple, I would rather avoid re-installing. Sooooo many games/software to reinstall. Any suggestions are hugely appreciated.

[Ekpah]

I think its booting sector got corrupted to malfunctioning that is why you are not getting it detected. Just check whether this is detected in BIOS or not. Install the Windows again in the same to create new boot sector and see whether this is working with the issue of yours or not. If you want previous installation of file same then it is better to create back of those file and then perform installation of new OS.