Joshua Kronengold

Nah -- the problem was that the keyboard and mouse had differend ribon connectors, and while the keyboard's connector worked just fine, the mouse's connector was just a bit to small to correctly attack to the laptop.

The old mouse (which did have a quite worn, but functional cover), by contrast, connected with a satisfying click that made it quite obvious that what had been going wrong was based not on my doing something wrong, but on the new mouse having a subtly wrong setup (a ribon that was both too short and the wrong shape) for the model of laptop I was installing it into.