Sony Vegas Pro 9 Problem

I just got this Sony Vegas Pro 9 last month, at first it all works fine, but it's working very slow.
One of my issues is when I closed the app normally with projects on it, everything will stop working, and the loading will stop at a specific percentage.
I tried to leave it for a while just to try if it works leaving it for a loading, but it actually didn't work. So I had to force shutdown the machine.
Also in rendering a video from veg. to .avi, it will stop in a percentage of rendering and everything froze, even in rendering it into a lower quality.
But one thing that puzzles me is that there is a time that it will work and sometimes it doesn't work?
Very strange. I still have a huge space in my memory, I have Win 7 with 2 GB of RAM.
Please help?
Thanks!
