Freezes, sometimes at blue screen, old iBook G4.

OK...old machine...iBook G4, 1.07 Ghz PPC, 768MB DDR SDRAM.

It always freezes, but does it at different places. Sometimes it’ll install completely, sometimes it won’t make it past the blue screen. I...

Zapped PRAM

Reset open firmware

Installed Tiger

Installed Panther (these were separate tries...HD was formatted before each)

Removed battery and tried it again

Dug into the machine and put a shiv beneath the heat sink

It definitely goes further after it’s been sitting a while, but when I wrap ice packs in towels and place them on top of the keyboard and beneath the machine, over and under the heatsink (hey, not like I can damage it too much now) it has no noticeable effect. Sometimes makes it past a blue screen, sometimes not (but it always lets me get into open firmware and zap PRAM.) Ideas?