Boot error: status: 0xc000000f - winload.exe missing or corrupt

I seem to have encountered a problem that a number of people have come across. It started when I was away from my computer and hit "Lock this computer" while I was away, as I often do. When I came back a couple hours later I logged back in and tried to open Firefox. Nothing happened, I hit ctrl+alt+del and it didn't come up. I waited and about thirty seconds later the screen came up with all the options (lock this computer, start task manager, etc.) and I opened task manager to see if Firefox was running and it wasn't. I closed task manager and went to restart my computer from the start menu but I couldn't. I don't exactly remember what happened at that point, but I do know I ended up having to hit the power button on the computer itself to shut down. It was late, so I just left it for the night. When I got home the next afternoon I turned on the computer and a black screen came up saying that the file "\Windows\system32\winload.exe" was "missing or corrupt" with the status 0xc000000f. It told me to repair from the disk, so I went into BIOS and set the first boot to the CD drive and put in the disk. At one of the screens that came up it said all the "Booting from CD" and "press any key to boot from CD" stuff, I press a key, and the next screen that comes up is the same black error screen. I've read other people who have had this problem could actually boot from the disc and repair, but I can't get anywhere.

Anyway, I don't recall making any changes to my computer that would cause this. I only have one hard drive, one OS (Vista Home Basic 64 bit), no partitions or anything. I built my computer at the end of June and haven't had a single problem since.

Any help would be massively appreciated. If you need any more information just ask.