Framework installation installs ASP.NET automatically only if IIS is already installed.if you install IIS after the Framework you need to manually register ASP.NET.
Go To C:\WINDOWS\Microsoft.NET\Framework\VERSION
[here C:\ is Windows installation drive on your machine.]
(e.g. VERSION is v2.0.50727)
You'll see there aspnet_regiis.exe.
Run that on command line with -i switch (e.g "aspnet_regiis -i"). That'll register ASP.NET to your machine as well as creates the ASPNET user.