Thanx all
I'll try replacing the PRAM battery. But I'm now wondering abt the OS.
A couple of other machines (Air, Ti Onyx ) have recently shown a tendency to have temporary blackouts, particularly if I leave them on sleep and the battery runs down. They come back after a few forced reboots, but they take their time, and it's scary while it happens.
I don't recall this happening in the old OS9 etc days. Then, you could tell what was happening at startup from the noises, time lag, etc, until the smiley face after the Apple chip had done its checks. OS problems would only show at that time.
So, I'm wondering if OSX might be the problem. Both the 400s are running 10.4. I think the Onyx is on 10.5.
Could this be an OSX bug?..... or a feature?