There are some solutions:
1) Are you using Skype? If you are, remove it completely, install Office and then install Skype again. This usually fixes the problem.
2) you don't have .NET installed,then installed it and than install ms ofiice.
3) Edit the registry. To edit the registry click on START, then RUN ... In the box that appears type REGEDIT and click OK. Browse down the following path:
HKEY_LOCAL_MACHINE > SOFTWARE > MICROSOFT > OFFICE
Delete the keys (items) you find in the OFFICE folder but not the sub-folders. This removes traces of previous installs to avoid possible conflicts when installing the new version of Office.
Then browse into:
HKEY_LOCAL_MACHINE > SOFTWARE > MICROSOFT > OFFICE > DELIVERY > SOURCEENGINE > DOWNLOADS
Delete the keys (items) you find here.