Sony PCG-F420 Primary User Manual page 69

This section describes how to solve common problems you may
encounter when using your computer. Many problems have simple
solutions, so try these suggestions before you call Sony Customer
Support.
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Check that the computer is plugged into a power source and that it is
turned on. Check that the power indicator on the front panel of the
computer indicates that the power is on.
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Check that the battery packs are inserted properly and that they are
charged.
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Make sure there is no diskette in the floppy disk drive.
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Confirm that the power cord and all cables are connected firmly, as
described in "Connecting Peripheral Devices" on page 43.
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If you plugged the computer into a power strip or UPS, make sure the
power strip or UPS is turned on and working.
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If you are using an external display, check that it is plugged into a
power source and turned on. Check that the brightness and contrast
controls are adjusted correctly. See the manual that came with your
display for details.
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Moisture condensation may have occurred. Do not use the computer
for at least one hour and then turn on the computer.