Once the OS has hung (blue screen, panic, etc.) there is no way through the OS to reboot the system.
Your only solution would be to install a remote management card, that would allow your to either dial-in or telnet into an interface that would allow your to either reboot or power cycle the system.
There is no way if we get a blue screen which for sure requires a powercycle. There are many remote managemnt devices on the market, we are using on our different data centers and thro which power cycle the servers if in case of issues or for any other requirement also. The initial investment if high but it serves the purpose for remote support.
BSOD blue screen of death