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UPS powers off but computer does not reboot after system is shutdown

"This issue is the result of a particular type of computer power switch generally found in ATX class motherboards. This document discusses the switch and how to configure the system to allow system reboot.


An APC UPS powers off after system shutdown and powers back on when normal power is restored. However, the computer system attached to the UPS does not reboot after normal power is restored.

Another symptom of the same problem occurs during a scheduled system shutdown/reboot. The system will shutdown at the proper time but will not reboot. This generally occurs with ATX class computer motherboards.


To ensure that the power switch is the problem run through the following test:

1. Boot the computer system up

2. Bring the computer system down to a safe state

2a. For Windows 95 shut the system down and wait for the ""It is okay to turn off the computer"" screen

2b. For Windows NT shut the system down and wait for the Restart button to appear

2c. For Windows and NetWare bring the system to a DOS prompt

3. Unplug the computer from whatever power source is currently in use

4. After the computer is turned off, plug the computer back into the same power source

5. If the system does not reboot the power switch is the root cause

6. If the system does reboot the power switch is not the root cause

If the problem is determined to be the power switch call the computer vendor to change the configuration of the power switch.

Most computer vendors are able to change the system BIOS or set a jumper on the system Motherboard to allow the switch to have a normally on position. When this is set the computer will reboot when power is restored.


Many computer vendors are using power switches that do not have a normally ""on"" position. This means the power switch must be pressed each time the computer is to reboot. These switches are not compatible with APC UPS systems."

APC Canada

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