There is a Technet Wiki page aimed at helping anyone who is experiencing problems with a Silverlight install.
Please visit this page:
http://social.technet.microsoft.com/wiki/contents/articles/30387.silverlight-trouble-shooting-installs.aspx
And follow the advice there before posting questions.
You will find some basic advice on troubleshooting, a page you can use to explore the issue and advice on what to include when asking questions.
Please follow the advice there initially and include any results when you post.
Thank you in advance.