I have three shapefiles and two buffers made from two separate shapefiles. I was trying to do a spatial join and it kept coming up with an empty file even though there was clearly overlap. I realized that some of the shapefiles had different projections. I changed them all to NAD 1984 for zone 18 and I also tried WGS, and then GCS WGS, but two of the shapefiles and a buffer file are now unaligned with a shapefile and its buffer. They are all the same coordinate system and they aren't aligning when they were before I changed the coordinate system. Is there a way to change them back? The undo button just says "remove layer." Or suggestions to fix this? I don't want to start from scratch with the original data.
If you are defining the projections with define projection or editing their properties then you will encounter this problem. What you want to do is Project to the coordinate system. This will modify the features to be in the new coordinate system and not just redefined and in the same place.
To define them back again just do what you did before in reverse.