Issues with uninstalling and re-installing SQL Server 2008 R2
Log in with your Windows account and enable the SA login again.  You'll probably need to configure the SQL Server for mixed mode authentication as well.

If you decide that you do want to reinstall SQL, after uninstalling it you'll need to remove the database files then you can reinstall.  SQL leaves the databases alone when you uninstall so that you don't loose any accounts or data when reinstalling.