Thank you for your post.
Are you all using/sharing the same database file? Or, is this a new database file?
If you create a new database file, are you able to enter/edit the information? If so, then return to the original file, pull down the View menu and select "Layout Mode". Click on one of the fields that is not allowing you entry, pull down the Format menu and select "Field/Control -> Behavior...". Make sure both boxes at the top are checked. That is, "Allow field to be entered" in Browse mode and in Find mode.
Any additional information you can provide may be helpful in determining the cause.
Creating a new database from a template on the affected computer would help eliminate doubt.
This problem occurs on all databases, even the template databases. I can provide no further information regarding this issue, was just curious if anyone else had encounter this problem.