Office XP

I installed Office XP Pro, on new Dell XPS system. For several months I had no issues. I shut down the PC for two vacation. When the PC was restarted, I have been unable to open any office file. I receive an error “file *the file name* is unavailable”. I reinstalled Office XP Pro several times, with same results. I also installed Office 2000 with no issues. I also reinstalled Windows XP Pro. I have tried to install service packs 1, 2 and 3, with 2 and 3 reporting “wrong version”. What are my options if any?