Try Booting into Windows Safe Mode
Before booting into safe mode, remove all CDs, DVDs, FLASH memory thumb drives, and turn off any external hard drives. Remove any floppy disk, too, if your PC has one.
In Vista, click Start, click the arrow at bottom right, and select “Restart." As the PC restarts, press and hold the F8 button. If the Windows logo appears, you’ve missed the opportunity and should try again. Select the operating system you want to start in safe mode (if more than one OS is installed) and then press F8 again. On the next screen, select Safe Mode and press Enter.
In Windows XP, click Start and click “Shut Down." Hold down the Ctrl key as the computer restarts. When the “Starting Windows" message appears, release the Ctrl key and press F8. Select Safe Mode and press Enter.
In Safe Mode, start Word 2007 and see if you can open your problematic documents. If this fixes the problems, then you have some sort of driver issue or application conflict. Safe Mode starts a very limited version of Windows with only the most basic system files and drivers open. What this step has done for us is to eliminate Windows default settings and basic system drivers as contributing to the problem.
If booting into safe mode resolves your problem, I'd suggest looking at your Word add-ins and plug-ins in the Trust Center. Start at the Office button/orb and select "Word Options" at the bottom of the dialog. Then check under "Add-Ins" and "Trust Center." Temporarily deactivating an add-in will rule it out as a source of problems. Some plug-ins are not readily visible. For those, select the Add-Ins tab and select Manage → COM add-ins →Go at the bottom of the dialog.
A variety of applications seem to like to plug into Word, so it's not possible to guess what you'll find. Look for applications that seem to have a minimal effect in Word or that you did not specifically authorize, and then test them, one by one, by disabling them.
If you find an add-in that conflicts, great! Your next step is to contact the manufacturer of the offending application to see if they have a program update or a fix for Word 2007.
If no conflicting add-ins or plug-ins were found, please continue troubleshooting.