This is a really odd problem which I've never encountered before, but I suspect that it may be due to dirty or faulty DX film speed contacts.
Try cleaning them, but I doubt that will cure it, so try manually overriding the DX fIlm speed coding by manually setting the ISO film speed setting. Unfortunately your camera doesn't really allow that so you have to fool it by placing a piece of thick paper over the DX contacts before inserting film. The camera will then select a default of ISO100.
You can download a manual
here.
If this does not fix your problem there is little you can do other than to replace the camera body with another; parts are no longer available and yours was a basic consumer level model which was never designed to be repaired. The high degree of electronic integration makes any kind of in depth repair very difficult and economically unviable.
It may help to know that as they are virtyually worthless, you can pick 35mm Dynax/Maxxums up for free or near nothing on FreeCycle/Freegle and auction websites.
Please let me know how you get on.