I haven't ever actually worked with panelware and don't know anything about them, but if the HMI program is stored on some kind of memory card, you should be able to just buy a replacement HMI on ebay and hope that it's a hardware issue and not a corrupt memory card issue.
Since you're talking about a PLC that has been obsolete for multiple decades, you might want to look to look to the future. If the OEM is still in business, they can probably retrofit the machine with a C70 and some X20. If not and you have a drawing set, any B&R integrator should be able to pull it off.