Downloaded file failed signature verification and may have been tampered with. Tried to install twice with no success. Same error. Any suggestions?

I have spend at least 6 hrs trying to install SQL Server 2008. I am not one to give up. But, I am exhausted trying to figure it out. I have read the pre-requisites and I think I am good to go. I do not know what my problem is. Can anybody please help me here? Here is the last few lines of my log file...

Greetings. Trying to install features via the web platform installer. SQL Server Express fails to install. Error code is -2067529721. Log below. Any suggestion on how to resolve this? Thank you. DownloadManager Information: 0 : Adding product SQL Server Express 2008 with Service Pack 1 ( www.microsoft...