Auto Reboot on System Crash

when the Windows XP operating system crashes an automatic reboot of the system occurs. While this behavior can be convenient, the downside is the error message accompanying the crash is not visible. Often times this information can be a great help in troubleshooting the source of the crash. This behavior can be modified in two ways; via the registry or using the System Properties property sheet.

Start Run Regedit

Registry Key: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlCrashControl

Modify/Create DWORD Value of Data type REG_DWORD Named AutoReboot
Setting for Value Data: 0 = AutoReboot Disabled / 1 = AutoReboot Enabled

Exit Registry / Reboot

Open System Properties via Start > Control Panel > Performance and Maintenance > System

System Properties may also be opened using the WinKey+Pause key combination

Select the Advanced tab and then click Settings in the Startup and Recovery section

In System Failure section, clear the checkbox next to Automatically Restart

Click OK and OK to exit

source:here