I've had this happen to me twice, all of a sudden Windows 8 refuses to boot and gives an error code of 0xC0000225 (or something) and anything you do won't fix it. The problem is that since for whatever reason Windows thinks there's no bootloader, it refuses to boot. Period. You can't even go into the recovery environment, which is my biggest complaint at Microsoft.
In any case, there's one way I've found to resolve this. If you have access to another computer, take out the affected computer's primary drive and find a way to mount it in the system (internally, externally, whatever). Then do the following:
- Open command prompt as an administrator
- Type in "diskpart"
- Type in "list disk". Find out which disk the affected drive is.
- Type in "select disk #", where # is the affected drive's number
- Type in "list partition", find the partition number of the system partition (it's usually 100MB, 200MB, or 300MB), then type in "select partition #", where # is the system partition's number.
- Type in "assign letter=z", assuming you don't have a Z: drive.
- Exit out of diskpart by pressing CTRL+C
- Type in BCDBoot [Drive letter of affected drive's Windows partition]:\Windows /S Z: /F UEFI
- So if the affected drive's Windows partition is say G:\, you would type in BCDBoot G:\Windows /S Z: /F UEFI
It should fix the bootloader. If you can get into a recovery environment on the affected computer, then this should work as well.