When I try to open an MS Office program, it says it "isn't install

Hi, when I try to open any of the MS Office programs it says eg. "Microsoft

Office Word has not been installed for the current user. Please run setup to

install the application".

All the office applications clearly are installed as I've been using them

for 5 months. I'm also the only user on my computer. I have run the setup,

tried to "repair" the program, and also uninstalled and installed it all to

no avail. The worst part is that to get help from Microsoft I have to get the

Product Identification Code, which I can't access without opening one of the

applications. Either that or pay £46, which is outrageous.

If anyone can help I would appreciate it greatly. Thanks