Hi,
1) Enter the following commands from a command prompt:
msiexec /unregister
msiexec /regserver
Run the tools--serial number & installation. If it dosen help go next.
2) Go to add/remove proram and click on change and check if you can add the serial number from there.
3) Incase if it still fails, Download the windows isntaller and check the result.
http://www.microsoft.com/downloads/details.aspx?FamilyID=5fbc5470-b259-4733-a914-a956122e08e8&DisplayLang=en