A disc with the driver arrived in the mail today. I tried to follow the instructions, but got slightly lost, so phoned Trevor who sold it to me, and asked him to talk me through it...I don't want to make any more mistakes! Rebooted and...I have my whole screen back!!!!!
And the disc he sent me apparently has all the drivers on, should I ever need them.
Thanks a million for all your help, guys. One of these days I must learn how to do more with computers than use them to proon!