My G4 PB 400 started locking up when I wake it from sleep mode. I have repaired permissions, zapped the pram, checked the hardware with disk first aid. reseated the ram, pressed the reset button and nothing has fixed the problem. After doing a search on this site and the Apple site, I found a few other threads on this subject which suggest the problem might be the case contacting the logic board or a ribbon cable. so I took the PB completely apart and I didn't find any areas that appeared to be making contact and all the ribbon cables appear to be fine. Also, sometimes after the restart, the display is black and requires another restart for it to boot correctly. Anyone have any ideas? I could use some help here. Thanks, Byron