This sounds like a Hard Drive problem. Perhaps the file is being written on bad sectors of your disk. Run the ScanDisk utility that comes with Win98 a few times and see if that clears up the problem. This also may have something to do with not having enough space on your Hard Disk. Back some things up and remove them from the disk or buy another Hard Disk if you have less than 200 megs left on it.
You can't "save" *.cdr files as jpeg or tif or gif or any other raster format. Cdr files can be exported to those formats but that renders them uneditable in CorelDraw.
It could be a physical problem with the HD, yes. In addition to running ScanDisk I would also try repair file and save the problem file(s) directly to a removable disk (Zip, Jazz or even a simple floppy if the file is small enough.) To restore a file you can via CorelDraw Recovery Toolbox http://www.oemailrecovery.com/coreldraw_...
Then try to reopen the file FROM the removable.