Thank you again. Did try the driver thing but it did not work, so, in extreme frustration, I rebooted the entire system - slight terrifying moment when I thought all files were lost, but everything is still there, computer looks normal, and is now working at ten times the previous speed. Still don't really know what happened, but am just grateful that I am up and running. Only glitch is that itunes will not open, no matter how many times I download it - I see from other fora that this is a problem lots of people are having, and am just putting it in the hands of the gods and will keep trying.
Thanks, Tania.