MS Office launching problem, encountered by error message

Hi,
For last few days I have encountered a problem about using MS Office on my desktop with Win XP Operating System. The problem is that, whenever I went to launch MS Word, I have got the following error message:
Runtime Error!
Program: C:Program FilesMicrosoft OfficeOffice12WINWORD.EXE
R6025
Pure virtual function call
After that, if I click on the OK button, the message disappears and thus I am unable to use MS Office anymore.
Can anyone please in this aspect to solve this problem?
