Check in IIS manger if the application pool and site are running. Check if the application pool is running with the correct account.
Also make those modifications in web.config and access again the site:
<SafeMode MaxControls="200" CallStack="true" ...>
<customErrors mode="Off" />
<compilation batch="true" debug="true">
This will help you to see ASP.NET exceptions and errors.
MCITP|MCTS SharePoint| SharePoint Performance blog