The power button cable is very fragile! You don't have to disconnect it to access the internals— but it will require you to keep the bottom cover propped up.

To disconnect the cable and remove the bottom cover, follow the next two steps.

If you don't disconnect the cable, prop up the bottom cover to prevent straining the cable and skip the next two steps.

Grip the power button cable close to the head and pull it away from its socket to disconnect it.