8b040810_el_Boot_Parameters___DataBook___2
[0] reboot=b [1] Kernel [2] 
I had a great deal of trouble finding this parameter. It is used for some motherboards which seem to hang during the reboot process, such as the ASUSTeK Computer INC P5S800-VM motherboard I have used on a few computers for customers. This parameter seems to allow the reboot to proceed normally.
Kernel Boot Parameters | DataBook®
2