If you can't find your company file, you can always restore a backup file. Follow the steps above to locate any backup files on your computer. See the AccountRight help for instructions on restoring backup files (Australia | New Zealand).
If you've run the Optimisation Assistant recently, a copy of your pre-optimised company file will have been created with the file extension changed from *.MYO to *.BAK.
Go to the folder where you normally store your AccountRight company file and look for files with a *.bak extension. When round, right-click the file and choose Rename and change the file extension from .bak to .myo. Then try opening the file in AccountRight to see if this company file is sufficiently current.