When you try and start in Normal mode what happens? If you see a blue screen then its likely a driver failure but your machine is not configured to dump and it simply reboots.
If so, in Safe mode do the following:
1. Right-click My Computer, and then click Properties .
2. On the Advanced tab, click Settings under Startup and Recovery.
3. Clear the Automatically restart check box under System failure, and then click OK
Restart the machine and see if it displays a STOP screen, this may indicate a driver. If so you can disable it.