Question : Laptop Crashing in Standby

I have a Dell Latitude D600 with XP Pro sp2
Recently my laptop has started crashing after entering standby mode.  Every time i close the lid of my laptop it will enter standby mode ok.  If i open the lid back up a couple moments later it comes out of standby mode ok.  When i close my laptop and put it in my back pack and take it around campus for the day the laptop turns off unexpectantly (it used to be able to stay in standby over night).When it is started back up i have the Reload my Active Desktop screen.  I have not been able to get the laptop to repeat the problem while it sits on the desk in front of me and i watch it in standby mode (this is so boring.)
I cant figure out if this is a software or a hardware problem.  Sometimes it will turn off for a five minture walk and others it will stay in standby for a couple hours.  I have checked windows update and have all the current drivers for my computer.  Is there a way i can see the last thing to happen before the computer crashes?  I checked Event Viewer but it stops when the laptop enters Standby mode.  What could be happening in standby mode to cause the computer to crash?
Could this be a hardware problem?  The laptop is over 3 years old, and the battery is getting old, but when i open the laptop after it crashes in standby mode the battery is still full (obviously because its been turned off and has not been draining the battery.)  I have ran all types of tests on the memory and fans and such with the bios and the only test that would not complete was the IDE Disk Drive Verify Test, which is a very time consuming test. (it kept restarting itself, but not necessarly failing.)
This is a hard problem because it occurs during standby mode when i cannot monitor the laptop.

Answer : Laptop Crashing in Standby

how old is the notebook?
Lithium batteries have a limited lifespan, although some last alot longer than 24 months, I've come to not expect that.  Stand-by consumes battery at a fixed rate, but if the battery's life span has been shortened by use, heat, abuse, then it may not make it through the night and leave windows in a improper shutdown state.