Can’t uninstall Microsoft SQL 2008

Here's the situation. I was trying to install Microsoft SQL Server 2008 in my laptop and it was a successful installation actually. But when I tried to start the MS SQL Server, it didn't show up like I expected. I couldn't write any query, and so on. So I get a new copy of MS SQL Server 2008 from my friend and was going to install this one. But when I tried to remove the old SQL, it denied and can't be uninstalled.
