Most of the Sony Mavica used a 3.5 Floppy Disk. Assuming yours is the Floppy Disk version, this is a hard to find media and is not a reliable as it used to be. You might get the camera to function again by getting a Floppy Disk cleaner. Make sure it is a Wet version not a Dry Head Cleaner.
Some times the loading mechanism is the cause of errors. It may need to be serviced and cleaned also. You could try inserting and ejecting the disk a few times rapidly to try seating the disk properly.
As for getting old photos off an old disk....first you will have to have a Floppy drive on your computer. If it is a newer computer chances are it does not have one. There are external USB Floppy drives available :
http://www.bestbuy.com/site/olspage...However if the Disk is damaged or has bad sectors you may not be able to retrieve many or any photos at all.
Again this is assuming yours is the Floppy Disk version. There were a few models that used a CD and you could try a head cleaner on these.