Now the other day I was going to play some Sanctum 2 with Alex and for some reason Steam decided that none of the games I had installed on my secondary D:\ drive were installed anymore. The game names were completely grayed out in Steam, yet I could verify the games had been installed by navigating to my D:\ drive using Windows Explorer. So what gives? Thankfully, this is a very easy fix! Basically, Steam has forgotten where these games are installed, so we just need to add a Steam Library folder entry into settings to remind it.
1. Open up steam, and under the Steam menu (top left on the window), go into Settings.
2. In the settings window, click “Downloads”.
3. At the top, you’ll see a heading called “Content Libraries”, underneath that is a button that says “Steam Library Folders”. Click that.
4. Next, click “Add Library Folder”, navigate to the folder where your games are installed on your secondary (or tertiary, etc.) hard drive. Close that window, and you’re done!
5. If you close the settings window and go back to your steam library, your games should be magically reinstalled!