Browser hangs / high CPU when starting ASP.NET project from Visual Studio 2010

For quite some time now I'm having problems to start ASP.NET projects from Visual Studio 2010 Professional SP1. I have all actual Windows updates installed. When I debug or start without debugging the browser only displays a white screen and in the status bar "waiting for answer of localhost". The address bar shows the correct page. The CPU goes up and the fan starts, but the page is not displayed. After some minutes IE displays that the webpage can't be displayd.

If I type in the local address in the browser address bar "localhost/path..." all applications run fine. (First I was not able to run the applications entering the page in the address bar due to missing access rights. I keep websites in the websites library) When I added IUSR and IIUSR... they run fine directly from the browser. Still I can't run or debug any application out of Visual Studio.

I created a new web application with ASP.Net 2 and 4 inside of Visual Studio. Still I wasn't able to debug or run them from within Visual Studio.

I tried turning of AV and Firewall (GData) and run VS explicit as Administrator—No difference. I tried to set the local IIS as the server, but still IE ramps up the CPU and IE only shows white. So the same problem occurs independet of using IIS or WebDev.

When I switch back to default server and run the page from VS the address bar doesn't show the page name and path anymore. Rather it shows the root folder of the web site project only. Even if I switch back to custom server IE only shows the root folder (localhost/virtdir). I need to restart VS to have it work again.

If I enter the same URL in a new browser window the page is displayed. So it seems it has nothing to do with WebDev, but rather with VS. Since I can attach the debugger process to IIS when the page is in the browser it seems not to be the debugger. I tested attaching the debug process to the IIS worker process. This works fine. I can also debug from within Visual Studio WinForms. The issue occurs only when I start aspx pages from within Visual Studio.

I can't recall the exact steps anymore, but if I'm not mistaken I had kind of the same problem before installing SP1. The difference was that it only occurred in one project and IE and VS hang completely. I had to kill both processes. I deleted VS settings files and it worked again. Then I installed SP1 reading about the debug problems. Now no website project works anymore.

I'm pulling my hair. I already wasted two days when I supposed to have finished this project.

Does anybody has an idea what the cause is?

Marcus