Lightroom did not do anything to your folders. The folders have been moved or renamed outside of Lightroom, or possibly the drive that the folders are on is disconnected. You need to find the folders using your operating system. Once you do that and you know their location, you can reconnect in Lightroom, right-click on the folder name and select Find Missing Folder and then select the location of the folders that you just found using your operating system.
Windows or Mac?
LR does not move folders on it's own. And if it does, it keeps track of that. That's how it should work...
Now what may have happened on a Windows system:
First: you may have moved a folder inadvertently into an other tree on the same disk. As this happens very fast, it can happen and the user does not notice it.
Second: Your drive changed the character from (P: to S: for example), because you attached an other external drive, and that one took the spot. Windows attributes those drive names on a first come first served base. If the character is taken, it allocate the next one. That character keeps being attached to the drive until the character is taken by some additional drive. This is very confusing and counter productive, not only for LR.
Fortuneatly it is easy to relink the files as shown in Julieanne's video.