Newly acquired, xp, sp3, all updates from ms applied. Latest T-vantage toolbox installed and hardware scan is unrevealing. Symptom is that when monitor turns off as specified in the power scheme I can't get it to come back on. Keyboard remains functional so I'm able to shut down or restart normally which restores the monitor to normal function. I've temporarily set the monitor to never turn off but it'd be nice to not have to resort permanently to that workaround. I haven't been able to find any settings in display properties that address this either. Any clues?

Turns out the onboard display adaptor is defective. After discovering that the issue only surfaced after changing resolution to higher than 800x600 I plugged a spare graphics card in and the issue was immediately resolved. I've got an RMA and am waiting for a replacement at the moment.