Could be that your main hard drive has become unreadable and unmountable, if you can boot to the install disk, if you can get to the command prompt, run a full CHKDSK from there and see if it has any errors, if it does, then go one step further and use whatever software comes with your Hard Drive make to run a full surface scan, if you have read element failure, it will cause this very thing. The Boot Sector is not on the main hard drive, so it gets so far before it says it cant find Winload.
Also, if you ever run a system repair via the hard Drive and the advanced boot options, you may be stuck in a boot loop, it may be looking for Winload on your recovery partition, which would explain why it is not the same version of Windows as your disk. Is there a recovery partition on that system?