Vista - Computer problems. Help please?

Hi. I've had this laptop for almost a year now, and just yesterday it started rebooting itself.
I have no idea why. Its in no particular pattern. I would be doing something like chatting, or playing a game, or writing some paper, and poof! The blue screen appears. It says something on crash shut down or crash booting...something with 'crash' in it. I'm not sure, since it disappears as quickly as it appeared. I have Norton Protection Center, and run scans every day. It notifies me of a virus and kills it.
So this shouldn't be happening. Can someone help me?

start button > right click computer > select advanced system settings on the left side of the page. select continue on the uac prompt.

on the pop up box, select the settings button in the startup and recovery section. on the new pop up box, unselect the box "automatically restart." this will prevent your computer from restarting when you experience the next blue screen.

this is the start--when you experience the next blue screen, write down what the screen states that cause the error and post that info here.

more often than not, if your computer has been running good for a while, for about a year as you state, and then it starts acting funny, it is due to something you did. remember just before you started experiencing these blue screens... did you install any new programs? did you install any new hardware (bluetooth dongle, usb webcam, etc)? have you let anyone use your computer who may have downloaded something or maybe inserted a usb flash drive? if you suspect a virus, make sure all of your definitions are up to date, reboot your computer into safe mode, and perform a virus scan.