Gateway E-5400 System Manual page 45

Turn off the computer, remove the cover, and make sure that all
cables inside the case are attached securely. Also, make sure that
the colored cable edges are aligned correctly and that the
connectors didn't miss any pins. Disconnect and reconnect the
cables. Close the case as described in Chapter 3, reconnect the
modem and power cords, then turn on the computer.
Turn off the computer, remove the cover and, if you have the
proper test equipment, make sure that the new battery has power.
(Although unlikely, your new battery may be defective.) Close the
case as described in Chapter 3, reconnect the modem and power
cords, then turn on the computer.
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System Components