Your camera uses xD memory cards, and they never have a physical locking switch.
Your problem is most likely due to having used the xD card in an external card reader. The host pc sometimes sets the xD card as a "read only" drive. If so you must go back to the host pc and connect the xD card again. If using Windows then click on My Computer and highlight the xD card. Right click and select Properties from the device menu. Uncheck the box marked Read Only.
If that's not the cause of your problem then try re-formatting the card in your camera. NEVER re-format it using a computer.
If those options both fail, try another xD card which is known to be fully functional in your camera. This will determine whether the camera or the card is at fault. The camera is too old to merit the cost of a professional repair, and there's nothing more to be done with a faulty xD card, so replace whichever item is faulty.
You may also wish to consult the user manual for your model which you can download for free from Olympus in .pdf format.
I hope that I've been of assistance, please take a moment to rate my speedy and free answer.