RESOLUTION 1:
1) Go to View Menu | Toad Options | Data Grids | Visual.
2) Enable the option "Size to Data". Make sure that you do NOT enable "Allow columns narrower than header width".
3) Click "Apply" and "OK" to accept the changes.
4) Now open a new SQL Editor and execute a SELECT statement. The results should not show any of the fields truncated.
RESOLUTION 2:
1) Exit out of Toad.
2) Locate the Toad.ini file, by default this file is located in "C:\Program Files\Quest Software\Toad for Oracle\User Files".
3) Rename this file to Toad.ini.old.
4) Restart Toad and retest the problem.