Issue Screen has no options and defaults to this setting even after a re-install of program from (add remove programs), currently cannot do any work.
This sounds like the user's fin.zup file has been corrupted.  The zup file contains the user's settings i.e. column widths, visible columns.  Delete this file to restore the system's default settings.  When the user launches Navision again their fin.zup file will be regenerated but they will have lost their settings.
- Do a system search of 'All files & folders'
- File name = *.zup
- Look in = Local Hard Drive (i.e. C:DRIVE)
- Make sure the search criteria includes 'Search System Folders, Hidden Files & Folders, and Subfolders'.
- Search
- Look for fin.zup and delete.  (Note: There may be more than one; delete all.)
- Restart Navision 
NOTE:  You may have to re-enter database and company fields when trying to open database and company.  Otherwise you may not be able to open any companies or incomplete company list, i.e. see only Cronus companies.

Microsoft has recognized this as an issue and resolved the issue in SP2.
A1)  Navigation Pane Expands To Full Size and Can Not Be Resized
Sometimes when a computer is locked or goes into screensaver mode with Navision open, the Navigation Pane would come up in Full Screen and could not be resized.
This has been corrected
Hot Fix was obtained for customer's who are not ready to implement Navision 4.0 SP2 at this point.  See KBA 154 for Update 1 for Microsoft Business Solutions - Navision 4.0 SP1.