Office Repair and Restore Point
Finally, you might consider a repair of the application before performing a last-gasp reinstallation.
Microsoft Office 2007 comes equipped with a repair tool, ideal if you cannot start Microsoft Office Outlook or any of the other applications in the suite.
To use this, go to the Office button in one of your other Office apps and go to Options > Resources > run Microsoft Office Diagnostics. Click Diagnose to begin the wizard that will begin a scan and check of all Office tools – this utility will reinstall any damaged components, potentially resolving any issues that you might have.
After a reboot, you should try Outlook 2007 once more – if it fails to open once more, you may need to resort to restoring a previously made restore point. If a restore point is available, this will wind back your entire PC to the state it was in on the specified date. Potentially this could cause you other problems so use with care.
To revert to a previous point, go to Start > Accessories > System Tools > System Restore and choose a restore point to go back to.