I have got Sony Vegas Movie Studio HD Platinum Pro 10, but it is continuously crashing!?

I bought this from Sony, and it came in disk. I successfully downloaded it onto my laptop. My laptop has 4GB memory. At first I thought that maybe my laptop was a bit full; so I deleted some applications, but it still crashes. Whenever I'm doing anything on it, be it playback, importing clips, looking at clips, searching for clips etc. it freezes up and says "Not Responding" it then says Vegas Movie Studio has to close or something. If someone could help that would be great! Cheers