Will not fully boot
2.2 GHz A1226 EMC2136
Machine will not fully boot. Starting up from TechTool Pro 5.0.7
The machine tones and takes twenty seconds for Apple to appear then seems to load for another 1 minute 40 seconds and the screen goes black although I can still hear it running. It does this from a fully charged battery, AC only or both. SMC reset. PRAM zapped three times, RAM reseated and also with just one stick. I pulled the hard drive and ran Disk Utilities on it from another mac and had no problems. It does have the Nvidia chip but since there is no distortions or color changes Apple won't take it. Any ideas? My customer is looking at a new logic board and I hate to do that. Anything? Help!