On Board Computer Does not Work

I started my car and it died on me but started right up. About 10 minutes of driving and it died again. This time would not start up again. I tried doing a diagnostic test with the on board computer but the check engine light is not working. Car was towed and mechanic is trying to figure out what the problem is but the on board computer is not giving up any information. Does anybody have any suggestions? I am hoping that it is not the computer itself.