If you run a pressure washer motor without water there is a high probability that you will ruin the pump. With only 5 hours on it I wouldn't think that the pump is ruined, but it is a possability. I have done some searching on it and find nothing with helping troubleshoot your problem. I did find an owners manual which has a 800 troubleshooting number that you can call for help. try giving it a go. Good luck.
http://www.generac-portables.com/service_support/owner_manuals/search_results.cfm?model_pw=1536
cholbach
October 2005