I just downloaded Dawnguard for the pc and everything was going fine. A little ways in, I added a mod from Skyrim Nexus to fix the Thieves Guild Hood for vampires bug. After I installed it via NMM, I got back on Skyrim and it looks like Dawnguard was completely uninstalled or something.

When I went to my save file, It gave me the message that certain files had been taken out or whatever, just like it does when you uninstall a mod. I'm now sure it was talking about dawnguard itself, because everything that dawnguard added was gone. Vampire armor, Vampire Lord power, Serana, everything. I'm not even a vampire anymore.

I uninstalled the TG Hood mod to see if that somehow did it, and its still uninstalled. Does anybody know how to fix this, or at least reinstall it?

dawn guard hates mods it seems

The mod part I can't help you with ( Xbox player ) but can't you just reinstall / redownload Dawnguard ? Just don't turn the mod on again

I'm going to try that. Its more than just Dawnguard though. When I downloaded it from Steam, it looked like it just merged with Skyrim and didn't give me a seperate Dawnguard file. So basically I'm going to have to completely uninstall and reinstall Skyrim.

Look in NMM under plugins. Do you see Dawnguard.esm listed there? Is it checked? Or start up Skyrim and look at data in the launcher and see if it's listed. Or go into Program Files(x86)/Steam/SteamApps/Common/Skyrim/Data You should see Dawnguard and Dawnguard.esm listed there.

I can't see that you have to uninstall Skyrim just to download Dawnguard again. Just go onto Steam and find Dawnguard and download again.

I couldn't find how to redownload Dawnguard by itself from Steam, which was my problem.

However, the problem is now solved. Went to data in the launcher and it was unchecked, so that fixed it. I have no idea how it happened.

Best part is, I decided the hood I so pain stakingly got that mod for looked stupid anyway, so it was all for nothing =P

Such is the risk when using Mods.

There are zero guarantees that any Mods will work with or not negatively affect the vanilla game or DLC's.

Sounds to me like that particular Mod is one that may not be useable on your machine when trying to play Dawnguard.