If restoring a backup working copy and a new install didn't fix the issue, most likely it's something on the computer itself. Have there been any other changes made on the machine, such as OS updates, or other software installed? Could something be running in the background & hogging system resources?
General troubleshooting steps if X-Plane crashes are: run the update option to fix any missing or corrupt default files, reset to default preferences, and remove any add ons..