You're working with hatches, and it seems to be causing CAD to freeze.
For example, you may have selected an existing hatch in a drawing and attempted to scroll down the list of hatches, but CAD froze partway through your scroll.
This issue commonly results from the presence of DGN hatch pattern files.
Navigate to the following folder path C:/Users/(user)/AppData/Roaming/Autodesk/AutoCAD 20**/R20.0/enu/Support
In this path, ** represents the year of your CAD installation. So if you have AutoCAD or F/X CAD 2015, the path will be C:/Users/(user)/AppData/Roaming/Autodesk/AutoCAD 2015/R20.0/enu/Support.
Sort the files in that folder by "Type." Select all AutoCAD Hatch Pattern Definition (.pat) files that start with the letters DGN. Put these files in a separate folder, and restart CAD.
You should now be able to work with hatches without CAD freezing.