Iphone randomly stopped working when i got up?

lock button won't work, phone will not turn off only go into a 'seizure' of black screen with apple logo. restored iphone 3g. and synced everything back onto it fine. also it's fully charged/can still text/call when plugged in. as well when i plug it in it shows the power off slide. and when i check for updates it tells me i have non and i'm up to date.
i know it's an iphone 3 or 3g , but not to sure


I've had a similar thing happen to my new iPhone 4S three times. It gets hot and doesn't respond to either button -- the screen remains completely off. I have to hold down both buttons for awhile until the Apple appears and then everything seems fine... until it happens again. Once it happened overnight, so I missed  my alarms. Another time, it was while I was at dinner.
Always it happens when the iPhone is on standby with the screen off and nothing particular happening with it. The iPhone 4S is brand new, hasn't been dropped, hasn't been messed with in any way.
Is there a way I can get a trace of what happened before I reset it? The system log (visible in "System Status" and other apps) starts with the reset, so it doesn't help here.