Word and Excel "document could not be registered"

It also says "it will not be possible to link other documents to this document." This what happens when trying to open a Word document. After these warnings Word opens without any problems and I don't see anything different, and the program works fine.
When trying to open an Excel file I get
"Windows Installer", "Preparing to Install"
This is followed by an error saying
"the Installer service could not be accessed. This can occur if you are running windows in Safe Mode or if the Installer service is not correctly installed. Contact your support person for help...."

I have recently done some changes to my services following an online guide but not sure who to either correct what I have changed or fix this current issue. Any help would be greatly appreciated.

XP Pro SP2