Every time 3DX opened up, a temp folder
3dx7Temp is created inside the default system Temp folder.
Sometimes it might get locked and/or corrupt causing 3DX to crash at start up.
So it has to be deleted manually.
A default system temp folder is normally located at: C:\Users\Your_USER_Name\AppData\Local\Temp
Otherwise the location can be gathered by running (WinKey+R) this:
cmd /k set t