It doesn't always do it but I wish it would never do it.
64 bit vista fwiw
It said something once about a power state something ... I don't know.
Your trouble is Vista. That was one of Microsoft's worst operating system.
In Vista, the power button action is sleep mode and not reboot.
You can chech you power settings from the control panel or by typing: - "
powercfg.cpl" in RUN dialog box or Start Menu Search box and press "Enter" key.
I suspect to sort this you will have to go to advanced power settings.
Click change power settings, then click on change advanced power settings. Now you can select the power settings you want.
I would advise going to Windows 7 which is much better than Vista. The best option is Windows 10. I love windows 10. I have migrated my HTPC from Windows 7 to 10. No need for Flash any more. Windows 10 will natively decode just about anything, including Dolby Digital Plus, which my pre/pro does not have the codec for.
I like it so much I'm about to order and new laptop, with Windows 10. This laptop is 6 yours old and getting long in the tooth.