I opened a file I had been working on in ArcMap 10.6.1, and all of my layers have red exclamation points next to them. All of the data is on my computer in the same folder.
I right-clicked, Data > Repair Data Source, and all of the original files are immediately shown in the same folder they have always been in. If I click the correct file and click "Add", I get the error - "Error repairing the data layer".
So I tried just re-adding the files, but I get another error. "Open Failed - Error opening feature class - Whitespace is not allowed at this location", and another - "Warning - Could not add specified data object to the map".
A different file gave a different error, "Number of shapes does not match the number of table records".
One of my files - a polyline layer with two features - works just fine, but the rest are broken.
The only thing that has changed between when I last opened it and now is fairly significant. My antivirus thought a system file was suspicious, so I opted to replace it instead of ignore it. The replacing didn't go well, and my computer would no longer boot up. I took it to a shop that reinstalled Windows. I don't see why it would affect the ArcMap files, but figured I should provide context. None of my other files on my computer have been changed.