The same problem happened to me. I've had my N900 since nov (uk here) woke one morning and no power & solid LED.
1st i took it to a nokia care point.... no luck. 2nd sent it off to nokia repair 3 weeks later N900 returned fixed... so i thought! Woke up next morning and same thing had happened!! To say i was cheesed off was an understatement!!!!
3rd rung nokia straight back complaining about their customer service, repair quality control etc etc.... It took them another week before they sent someone to collect it. Another 2 weeks passed & i was issued with a new N900!
So my advice would be to send it off, demand a new one and prepare for a long wait!!
Oh i hope you've backed up your data? I didn't! Another crucial mistake!!!