Will not save to memory card

I have used the camera for a year or so with no problems. Lent it to my son for several months, no problems.  When I used it recently it would take pictures and after taking 7, it said memory stick is full. It will not save to the 1 GB memory card that we have used since purchasing it. 
I read the book and it says the card my be turned off, but can not figure out how to turn it on. It seems to be inserted properly, and again, it has worked in the past.
Thanks for any help you can give me.