Symptoms when booted in OS X: - touchpad does not control pointer at all - clicks of button will sometimes register - attached mouse works fine Symptoms when running built in diagnostics (hold down D on startup): - touchpad tries to move pointer, it jumps around and is uncontrollable - clicks of button will register (didn't test extensively) - attached mouse works fine. I'm assuming that the OS disables the touchpad when it sees that it's not behaving well. The pointer jumps around at the boot selection screen (hold down Option on startup). Background: This machine was repaired by it's college-aged owner who had cracked the screen. She ordered a replacement screen and put it in herself. The screen works but everything is not flush and lined up. I originally thought that maybe the internal connection was loose. Now I think the touchpad is defective. Other observations: When running the built in diagnostics the first time I got the error: "4SNS/1/40000000: 'TCOP'". A quick google of that error talked about issues that didn't appear related. After I disassembled the machine to get to the keyboard / touchpad top and ran the test 2x with it laying loose I didn't get any errors on the tests. Couldn't boot from a DVD until I took the keyboard / touchpad top off. Each time I tried the disc was ejected. After disassembly I could boot from the DVD. I don't know what kind of hit the machine took to break the screen, so I don't have a feel for what else may have been damaged. Should I be concerned about the booting from DVD issue and / or the one time error on the test? Is it reasonable to assume that if I order a replacement keyboard / touchpad top for this machine that I'll have a working system again?