C.S.I. dom game freezing

[Jabba]

Hi Fellow Gamers and Experts

I am having a problem with C.S.I. Dimensions of Murder, I played the first level okay, when I wanted to play the second level the game kept freezing, you could hear the sound but the picture froze. I had to keep using Ctrl Alt delete to get out of the game, I got fed up of this and tried to restart the level, this worked and was able to finish second level. Now, I want to move on to the third level, it starts to load, Grissom starts to tell about the “Bloody Case” and game locks up again.
I have run the programme “Can I play This” and my PC passes with flying colours.
My PC specs are AMD Sempron 1.67 ghz, 1gb of ram my graphics card is a Nvidia Ge Force 7300gt.
I can’t understand how the game can let me play the levels some of the time, surely, if there was a problem with my specs it wouldn’t let me play at all. Also, reading on the forum you advise to shut down any programmes running in the background, I run Norton Anti-virus and this is not possible, I would have thought the game and this should run together, have you any ideas?
Also, looking on the Forum it could be problem with Saved game, I can send you my saved game files if you wish.
Thanks in advance
JABBA