When the program is coming out of full screen, the reason it's automatically rebooting is because it's set to automatically reboot on a system crash instead of displaying the BSOD. To disable this so you actually see the BSOD, go to the System applet in the control panel, advanced, startup and recovery, advanced, and untick Automatically Restart. Then you'll at least be able to see the BSOD, and check my post here:
http://www.betaone.net/forums/index....ST&f=9&t=17498
to see how to analyze the crash dump it leaves for more info.
As far as not being able to warm reboot, have you updated any drivers lately? Did the problem start right after you installed SP3 or not?