Use Windows Update to make sure you computer has all the latest updates and hot fixes from Microsoft. Windows Help shows how to do this, or the the following article will get you started:
Note that updating can take some time if you haven't done this for a while. If the program runs after doing this step, then you do not need to proceed with the following steps.
Repair the .NET Framework
Download the Microsoft .NET Framework Repair Tool from Microsoft's website here:
If you are asked to select the download, select the file NetFxReapirTool.exe and click Next:
Run the downloaded file and follow the on-screen instructions.