Software Vanishing?

I have an iMac that had Microsoft Offic on the Mac loaded on it functioning fine. Out of the blue, yesterday, my dock Word, Excel, Powerpoint etc. icons have all changed to "?"s. I cannot seem to find the program in Finder , under applications or anywhere else. Even looked in trash to see if somewhow it got deleted.

Ifind this quite odd and a complete mystery. The program has been on the machine for over 3 years.

This forum has some very bright minds. Any ideas? I no longer have the original instal discs.

Brian