I made a stupid mistake yesterday. I was initiating a drive through a docking station on my laptop, and noticed a 'mark as active drive' option in the activation menu that I wasn't sure I'd seen before.
So I clicked it.
What this does is apparently make this particular partition the boot partition of the drive, and unless you have an operating system on that particular partition then you probably done messed up good.
I read the little help snippet after I'd done this, and rapidly changed back to what I thought was the original partition (the C drive, right?), and thought all would be good again. Seemed like nothing had happened after all. I kept using the computer that day, and today... it wouldn't boot.
Missing boot file.
I should mention I didn't even get a warning during the first change, but I did get a warning when I was changing back, telling me the implications of this dangerous procedure. That if I wasn't choosing a drive with an operating system on it then it'd be fucked up totally.
Needless to say I was pretty distressed about this new message, turned to Google on my regular computer, found a bunch of third-party solutions trying to sell particular recovery software products, a few commandline answers on Super User, and then I found Hiren’s BootCD PE.
I formatted a USB key, installed the ISO, and booted it on my laptop.
It's basically a little miniature OS, made to look like Windows 10, with a wide repertoire of programs that help you with all sorts of computer repair-related tasks, and basic software for anything else, like writing or browsing the web. It's barely a gig large, but works like its own enclosed OS, straight via USB, and though I didn't try any network-related tasks I assume you could as well use this instead of your regular OS.
I assume you can save additional files to the USB stick too if you have some space left. It's basically like Chrome OS but better, in that you can actually manage the hardware that powers it, use it as a dual boot, or carry your entire OS with you between computers.
I'm sure you can do this same thing with a lot of Linux-based OS:s, but I for one am not that accustomed to it, so this was pretty cool.
I tried some MBR and recovery-related apps, since that was my main purpose with using it after all, but that didn't help at all. I tried booting again a few times. Nope. The error message asked me for a Windows Recovery CD, which I didn't think I had - which is why I resorted to Google and alternative methods, but I decided to do some digging around anyway since the above (or my skills in using it) didn't seem sufficient to solve the issue... and what do you know! I had one lying around after all.
Booted with the CD, ran a system recovery thing, and there you go, problem solved. It wasn't such a difficult task after all. Just took me a couple hours to get it all working again.
Moral of the story: don't mess with settings you don't know anything about, and get a recovery CD if you don't already have one.