Unity Application freeze on build won't load project again

Oi. This is beginning to get really frustrating. Between yesterday and today I've spent a lot of time trying to troubleshoot this. Essentially when I build my scripts sometimes Unity will hang/freeze and then I have to shut it down through the Task Manager (end process). After that I cannot load that project anymore. Unity loads the project selection window, I can create and load other projects but if I try that particular project, the project selection window disappears like its going to load but it doesn't. I checked checking the task manager, and there's an instance of Unity for every time I tried opening that project.

Now I haven't had a crash yet but if I ignore the processes in memory (say waiting to see if its just thinking, it will finish loading eventually) Task Man says shows the memory Unity is using increases to something like 279,000.

Not sure if that's normal or not.

I'm on windows 7 64-bit.