Microsoft office 2000 and 2003

I installed 2003 on my computer but was unable to activate it as it was my housemates. I then tried to uninstall it to get back to my microsoft office 2000. but it didn’t work and didn’t let me open any of my files. I then tried to restore my computer to before I installed it but this also didnt work. now my files dont open. i dont have the disk as it came installed on my computer but i do have the installation key. what should i do? please help!! i desperately need it to do my work. cheers. xxx