With the release of Silverlight 5 Beta, you may be having trouble with specific websites crashing. As typical, beta software is still buggy and can cause problems since this software is meant for testers. Sometimes even full releases of software can cause system crashes and problems and conflict with something else on your computer. If at any point of time you want to downgrade Silverlight to Silverlight 4, you must first uninstall the newer software.
Click "Start" and go to "Control Panel" on your computer.
Click "Remove Programs" and scroll the list for Microsoft Silverlight. Click Microsoft Silverlight and click "Remove/Change Program" at the top of the window. Wait for the program to be removed from the list, showing that it is gone.
Navigate to Microsoft Silverlight 4 download page (see Resources) using your web browser.
Click on the "Click to Install" button and wait until the download and installation is complete. Close and reopen your browser to have Silverlight 4 active.