Progress dial freezes when booting from any HD

Hello! I'm going through some aluminum PowerBooks, and I've found a couple that freeze on the Apple screen with the progress dial. Option mode and target mode work, and I was able to re-image the drive in Target mode from another machine, but when it tries to boot, it freezes again. It also freezes when I try to boot from an external hard drive connected to the machines via FireWire. I've swapped the internal drive with another drive that has Leopard on it, but that also freezes when it tries to boot. I've tried all the resets, memory, etc., to no avail. I'd say the logic boards are defective, except that the machines came to me with Tiger installed, and they booted up into the OS 100% when they had Tiger. I've tried putting Tiger back on in various ways, with no luck. But because I did witness them working with Tiger initially, I'm convinced it's not a hardware issue, but something I'm not doing right (or something I'm doing that they don't like, anyway). It almost makes me think they are in need of a firmware update in order to take Leopard, although I've never known an aluminum (or any Mac) to require that.

Thanks!