Error "invalid product key" after installing Office Suite

Hi,, I am using Ms Office 2007 on my Windows Vista system. Yesterday i downloaded and installed Microsoft Office suit 2007. i don't know whats gone wrong after that, Whenever i am trying to open any of the office program, it gives me error message saying "invalid product key". Whats the problem ? Please help me guys.

Most probably the cause for this error may be trial version of an Office 2007 suite is installed on the computer. The computer manufacturer may have preinstalled a trial version of an Office 2007 suite. You may receive the error message in the "Symptoms of the problem" section if you did not uninstall a trial version of Office 2007 before you installed a retail version of Office 2007.

So to fix this error you need to remove the previously installed Office suite or individual programs. Then, do one of the following:

• Install the version of Microsoft Office that you want.
• Start an Office program if the version of Office that you want is already installed.

I think you need to remove Office suites or individual programs from your system. To do so, just follow these steps:-

1. In the Currently installed programs list, locate and then click either the previously installed Office suite or the individual Office program.
   
   
2. Remember that this includes any trial versions of Office 2007 that were preinstalled by the computer manufacturer. For example, the computer manufacturer may have preinstalled 2007 Microsoft Office system or Office 2007 Home & Student Trial.
   
   
3. Click Remove.
   
   
4. Click Yes when you are prompted to confirm that you want to remove the Office suite or individual program.

Retail versions of Office are self-repairing. To repair the version of Office that is installed, start any Office program and follow the instructions to enter the product key. To do this, follow these steps:

Exit any programs that are running and close all open windows.
Start an Office program. For example, start Microsoft Office Word or Microsoft Office Excel.
Type the product key for the retail version of Office when you are prompted.