TFS 2013 error - Service Unavailable 503

I have local installation of TFS Express 2013 on my machine. All of a sudden it started giving this error “Service Unavailable 503” when I tried to open Visual Studio Team explorer.

I thought something got corrupted as I was trying to install some other Visual studio updates. So I re-installed TFS but got same error.

After searching online, I cam across this one here.

So indeed my TFS application pool was stopped. I restarted the AppPool but noticed as soon as I try to access my local tfs via webclient it would stop the AppPool again.

That reminded me to look at the EventViewer and I saw the real error that was causing the site to crash. Some how my machine.config got corrupted when I was changing the mailsettings.

After correcting that error, TFS started working.