Are you seeing the red exclamation mark next to the layers in Table of Content. If yes, then repair the data source.
If the Repair/Set data source doesn't work, then check the following.
Open a blank MXD. And add the data from the new folder location. If the data is opening properly, then do the following.
Open the older MXD, Right-click each layer > Save as layer. Save it in a folder.
Open the new MXDs where data is displayed properly. You can import the symbology from the saved layer files.
NOTE: I would recommend saving the data in a more consistent folder (e.g. D:\Data or C:\Project\Data)
Think Location