IBM THINKPAD S05L-1270-01 - Manual (Page 290)

Be careful
Connect the CPU card using the exact procedure
shown in the figures, and make sure that the two
CPU card connectors are connected properly. If
these connectors are not connected, you cannot
power on the computer.
Do not apply any extra force to the shaded
area of the CPU card when connecting.
278 IBM Mobile Systems HMM