.NET Freeze

Hi People, I am all of a sudden having a problem with .NET freezing when I try to build and run a solution, it just hangs after the build 1 errors 0 line in the output just when the main form should open, I have to close it via task manager. This happens with all solutions, even if a create a new windows project and press F5 straight away. Has any one had this, or heard of this before, if so can you please help. Many thanks, Craig