I uninstalled and re-installed steam. I didn’t uninstall my games, and they still exist on my hard drive (I checked).
I have an SSD and a HDD, and to save space I install programs (including steam) to
C:\Program Files (x86)\Steamdrive (SSD) and games to
D:\Games\SteamApps(HDD). How to I let steam know the programs are installed there?
There is now an official support article at support.steampowered.com covering some other solutions as well.
Go to Steam > Settings > Downloads tab > Steam library folders. Add the
D:\Games folder there and restart Steam. Steam should then be able to find the installed games again.