One of our notebooks (IBM ThinkPad T42 from pre-Lenovo days) - running Windows - has started intermittently losing power. No STOP message. Nothing in the Event Log. Just blacks-out and reboots.
I suspect overheating CPU since it only seems to black-out when on AC power. On battery the Power Management switches the CPU to slow-speed and so far I haven't experienced a black-out like this. The battery condition is good and it will run several hours on battery alone.
I've checked the fan unit. The fan is spinning at what appears to be full-speed and quietly. I've removed the fan module, checked the thermal paste between it and the CPU surface, and remounted it firmly.
I've set the CPU to slow speed in the BIOS but this appears to be overridden by the IBM Power Scheme Settings after bootup. The control panel wont accept anything but "Maximum" for the CPU speed in the AC mode.
This notebook recently had a problem with it's internal Intel PRO/Wireless LAN adapter. Which was solved by upgrading drivers. That problem caused intermittent crashes with BSOD. Is it possible the Wireless card is physically damaged and with the new drivers is causing black-out-power-off instead of BSOD?