This is a device construction error. It sounds like the unit wasn't fully powered down before you started pulling head cables. It "could" be a blown fuse on the head dotter board, but I will have to do more research into it.
Run a search on these forums, there's some information concerning a possible solution to this problem.
ie: downgrading your firmware. powering down a couple times. You never know, this forum is a great resource for information.