You probably have seen this error:
Server Error in '/' Application.
Version Information: Microsoft .NET Framework Version:2.0.50727.4952; ASP.NET Version:2.0.50727.4955
The resource cannot be found.
Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable. Please review the following URL and make sure that it is spelled correctly.

Requested URL: /Pages/default.aspx

To see the stack trace, look at the HTML-source, after the </html>-tag the error is shown in comments!

[FileNotFoundException]: The file /_catalogs/masterpage/Product.aspx does not exist.

at Microsoft.SharePoint.ApplicationRuntime.SPRequestModuleData.GetWebPartPageData(HttpContext context, String path, Boolean throwIfFileNotFound)
at Microsoft.SharePoint.ApplicationRuntime.SPVirtualFile.CalculateFileDependencies(HttpContext context, SPRequestModuleData basicRequestData, ICollection& directDependencies, ICollection& childDependencies)
at Microsoft.SharePoint.ApplicationRuntime.SPDatabaseFile.EnsureDependencies(HttpContext context, SPRequestModuleData requestData)
at Microsoft.SharePoint.ApplicationRuntime.SPDatabaseFile.EnsureCacheKeyAndViewStateHash(HttpContext context, SPRequestModuleData requestData)
at Microsoft.SharePoint.ApplicationRuntime.SPDatabaseFile.GetVirtualPathProviderCacheKey(HttpContext context, SPRequestModuleData requestData)
at Microsoft.SharePoint.ApplicationRuntime.SPVirtualPathProvider.GetCacheKey(String virtualPath)
at Microsoft.SharePoint.Publishing.Internal.CmsVirtualPathProvider.GetCacheKey(String virtualPath)
at System.Web.Compilation.BuildManager.GetCacheKeyFromVirtualPath(VirtualPath virtualPath, Boolean& keyFromVPP)
at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
at System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean noAssert)
at System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath virtualPath, Type requiredBaseType, HttpContext context, Boolean allowCrossApp, Boolean noAssert)
at System.Web.UI.PageHandlerFactory.GetHandlerHelper(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath)
at System.Web.HttpApplication.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
[HttpException]: Exception of type 'System.Web.HttpException' was thrown.
at System.Web.HttpApplication.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)