"File Not Found" error in SharePoint 2010

You open your SharePoint site page and see "File Not Found". You have no clue what's went wrong.

This issue might be caused due to following actions:
1. Retracted any solution package from SharePoint site
2. Deactivated any feature.

If you have taken any of the action mentioned above then you needn't to worry as things are under control.

Now, try to open following pages:
http://<site name : port>/_layouts/managefeatures.aspx?Scope=Site
http://<site name : port>/_layouts/viewlsts.aspx

You should be able to open above pages.

If yes (or even no :)), just re-deploy the solution or re-activate the feature and you are good to go.

What went wrong when you took any of the action mentioned above?

Your solution package or feature are responsible for deploying any custom master page, custom control or some thing which was being referenced by SharePoint site. When you retract solution package or deactivate the feature, site doesn't find those components and shows "File Not Found" error.

Even if this doesn't solve your problem, you will find lots of other solution so keep your hopes alive. All the best!