Why do you receive a 404 when trying to visit Default.aspx on your SharePoint Site ( among other multiple reasons) ?
Answer ( among other potential answers ) :)
The site might reside at the root of a Wildcard inclusion managed path.
Managed Path at /ManPath/
The Default page at http://SharePoint/ManPath/Default.aspx
When you try to access the site, you receive a 404 (Page not found)
Remove the managed path through UI or powershell
$wa = Get-SPWebApplication -identity http://SharePoint
How do you end-up in this ?
Well, by creating a managed path at the same URL as your newly created TeamSite
thx for solution :)
Another reason this occurs is if you have a SharePoint 2010 site that was based on one of the Fab40 templates in SharePoint 2007 and was subsequently upgraded. A database attach upgrade will result in the site being there, so to speak, but being inaccessible due to the invalid site template. SharePoint doesn't actually throw any useful UI errors to let you know that, but digging deep enough into the logs, you can identify the issue.
For me was a corrupt Default.aspx page.Open Sharepoint Designer, go to a site thats working and browse all files, copy the content of the Default.aspx page.Then open broken site, browse all files, delete Default.aspx page, recreate it with copied html. Voila!