I tried your last suggestion yesterday with the device manager etc. but unfortunately I still get the freeze on shutdown once NIS 2013 is installed.
I will probably reinstall 2012 and hopefully that will work using your download link. I'm not sure I should persevere with the forced shutdowns, it doesn't seem healthy for my pc.
I downloaded a program called Steam to play a game. I thought that was the problem and removed it, but my computer keeps crashing and I can't use Norton.
thanks for the comments. Incidentally, yes I regularly defragment my hard drive (apparently Vista does this automatically behind the scenes, mine is scheduled once a week).
I have now uninstalled NIS 2013 and reinstalled NIS 2012 following yank's instructions and link. The freeze problem has gone and my pc seems to be back to normal regarding these issues. IE is not crawling anymore than usual and Steam uploads fairly promptly. it seems the new NIS 2013 build didn't agree with my four year old pc for some reason, and its not an issue with an update.