I have an apple powerbook g4 S/N W841827JQHX, 1.33Ghz 2g ram. Osx 10.4.11 It boots to a blue screen with cursor. I have tried various methods to fix it.( holding various keys whilst booting etc).I dont have any disks. Do I need to buy a install CD. The Tiger Osx Dvds, Or do I need to buy a Disk Doctor type program, I am quite happy to wipe system and reload Osx. Though am unsure what software is needed. Please can you help. many thanks Phil