Preloaded does not mean you did not get the disk. Office costs extra and always comes with a disk. It's too late now to complain about not receiving it. Your installation sounds like it is corrupted and without the  original disk, you're out of luck. You might try looking again through all those disks that came with the computer. You can try Add-remove programs, go to Office and select Repair. It will probably still ask for the disk, but worth a try. You also need the product key that came on the disk packaging.