My wife's N900 has been experiencing unexpected shutdowns for the last two weeks. Reflashing has not fixed the problem. Is there a log file that would help me figure out what is causing this?
Any ideas? This is random and can happen even when sitting on a desk or charging.
I worry that it is a loose connection if not software since it persists through a reflash, what components need to come off of the board to safely do a solder reflow?

Is it overclocked? Could be the reason.
If not, maybe the battery is loose? (although from what you said it rebooted even when sitting on a desk... so it probably isn't)

Can't really think of what else could be causing it, I never really had reboot issues with the exception of unstable OC / software mess-up

You may want to check your battery. I had a shutdown problem which this solved.

I had considered that as it is clocked to 800max, though it almost always shuts down while in screen saver with no apps running so throttled way down.

What is interesting is that I have to pull the battery to get it to boot so I dont think it is a contact issue, though I will check.

That is what we call overclocked.

Screen saver? Are we talking about the same phone?

That is exactly what suggests a contact issue. Please do check.

Pichlo, sorry, was writing and saw that I had added overclock to 800 when I had flashed using my phone's backup, no OC before.
Screen saver/blank/sleep whatever, it is dark but booted on standby sitting on a desk waiting for calls when it ends up having its problem
I will check connections once I have completed a battery calibration in progress.

Would also guess contacts.
Bend them out a bit. And clean contacts with isopropylen alcohol.

800 MHz should be on the safe side, mine is clocked to 800/850 since a few years (but no more)

i have similar problem from several days with my phone.I trying with;
*cold flashing
*resize partitions
*change 2 bat.
*advice from xman did not help me(by the way big thanks to freemangordon for everything)
*flasnig few times under linux
*from x-trrminal with commands reboot -d 0 and poweroof -d 0
*install droid and from power menu i puch reboot and shutdown

Finally i changed the board from my second phone(damage usb port) and voila the phone has been fixed.So if we have anything different from what i am done,please tell me.
regards
note:i forgot to mention when display turn off or i lock the phone,immediately follows reboot,olso i tryng with syslog(start sysklogd under root)but nothing happen,the reboot continue

Thought the battery connection tweak had worked until late today her phone died again. It does give an unexpected reboot flag on bootup after removing and replacing battery so it is apparently not something calling for a system halt.