Very odd USB problem - iBook G3

Hi all, I took apart my iBook G3 (as with this thread) to swap Hard Drives.

However, I discovered to my surprise that my USB ports worked again. With the case off the computer, the USB ports work perfectly fine..however when I put the case back on the computer, I found that the USB ports didn't transmit data, just run power through it.

Any ideas?

See, I don't imagine it would be a cable squash, as the USB Ports feed straight into the logic board, no cables or anything.

Heat is definitely a possibility, the little machine gets seriously overheated these days at times...but the only thing that ran noticably hot was the old hard drive, which I've now swapped out for a new one (It runs cooler and better).

That being said, I might just have to disassemble the bugger again. I suppose I could remove the internal metal casing over the thing...but apart from running the laptop open, I can't really think of much to do.