Grey Apple screen after updating 10.5.2

I updated my computer G5 1.8 Imac with the new update. The computer was running really loud and then was frozen so I had to restart it. Now it just sits on the grey apple screen with the circle loading icon going around and around. This was left on for 30 minutes with no change. Could somebody please help? What are my options to get my computer back up and running. I was planing on getting a new Imac next month and giving my G5 to my daughter, so I still need to correct this problem. Can I start it up with the Leopard disk? Need help please!!