Computer does not recognize my camera

Hi, I have a Cannon A720 IS digital camera. Few days ago i could download pictures to my computer but now it does not work i don' t know why. I have Windows Vista in my system. My USB thumb drive work properly but my camera and my cell phone does not connect to my computer. I don't think so it's because of Window Vista because i used to download pictures fews day ago but suddenly it doesn't, why? Please advice.
Thanks,
Jagjeet