Hello Colleen and welcome to Seven Forums. Disclaimer: I'm not an expert in sewing or embroidery. Heck, I'm not an expert at anything. But it definitely sounds like the software used to open/read the .pes files has become corrupt. So I have to ask, did your sewing machine come with an installation disk or setup disk that might be able to repair or reinstall the corrupted software?
From what I could find, the .pes file type is primarily associated with 'Brother/Babylock/Bernina Home Embroidery Format' by Buzz Tools Plus. I don't know if that means the software is proprietary. I also found this forum thread that may help. How do you open PES file?
One of the free utilities recommended in this thread is Wilcom Truesizer. It's supposed to be a universal file conversion tool and is able to read and convert many popular industrial and home expanded/condensed file formats including .pes files. Wilcom - Wilcom TrueSizer
Hope some of this helps. If it doesn't, my apologies for taking up your time.