Norton Antivirus has a Word plugin that is known to cause problems with opening documents and slowing down computers using it.
The first thing you might want to try is running the Live Update option of Norton and installing all it finds. This may update the plugin and solve the problem.
If that doesn't do it, you can turn off the plugin by following these steps:
1. Start Norton AntiVirus.
2. If Norton AntiVirus is part of Norton Internet Security or Norton SystemWorks, then start that program.
3. Click Options.
4. In the left pane, click Miscellaneous.
5. In the right pane, under "How to keep Microsoft Office documents protected," uncheck Enable Office plug-in.
6. Click OK