Gateway E-4400 System Manual page 53

Turn off the computer, remove the cover, and verify that all cables inside
the case are attached securely. Also, make sure that the colored cable edges
are aligned correctly and that the connectors did not miss any pins.
Disconnect and reconnect the cables, then replace the cover carefully, so
as not to disturb any cables.
Turn off the computer, remove the cover and, if you have the proper test
equipment, verify that the new battery has power. (Although highly
unlikely, your new battery could be defective.)
When everything works properly, close the case (see "Closing the case" on
page 19), reconnect the modem and power cords, and turn on the computer.
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System Components