Before attempting this, realize that any customized settings, toolbars, etc, will be lost if it fixes the problem.
If you have done a lot of toolbar customization you can try to save them, that you can restore them afterwards.
Press ones short the Windows-Key
Type "regedit" and hit Enter
Within the Regestry press few times the arrow directing left on your keyboard, to move to the highest level
Select HKEY_CURRENT_USER and press the arrow directing right
Press s to jump to the entries starting with s and go down to Software to open this as well
when you are in Software press s again and go down to Solidworks, Rename this file from SolidWorks to SolidWorksOLD
Start SWX (a new Solidworks-Registry-Key will be created) & check if Materials is accessible
If it is you can return to registry and delete the entire SolidWorksOLD
If that did not fix the problem, return to registry, delete the new SolidWorks key, and rename SolidWorksOLD back to SolidWorks. This should return all customization.
I had similar Problems, when I wasn't logged in as Administrator.
Do You have Admin rights?
There could be an issue with your material database environment. Resetting customized settings or logging in through a different user account may temporarily resolve the behavior simply because you are starting with a new default material database environment (e.g. no additional file locations for materials, etc.).
The best long-term resolution is to review your current material database environment and implement best practices to avoid future issues. Take a look at S-072674 in the SOLIDWORKS Knowledge Base (KB) for details and please be sure to contact your SOLIDWORKS Value Added Reseller (VAR) for further assistance if necessary.
This is the exact same thing that happened to me. My solution was easy to implement so I hope it works for you.
I had duplicates of the materials that I was trying to apply that created themselves in my Custom Materials folder.
For example, if I am trying to apply 6061-T6 and it shares the same name in my Solidworks Materials folder then the software doesn't know which one to choose so it fails and closes the window. I deleted the version in my custom materials database and was successfully able to apply the material after that. This took me a long time on the phone with my VAR and it was escalated to SW technical support to find the solution.
Let me know if that works for you, good luck!