cannot reboot using su reboot when usb not plugged ?

[skprod]

hi.. i got an haipad 701 2.1 rooted

i coded an application that make my pad reboot at 5hours am. with runtime exec su reboot now...

But when usb is not plugged, the pad just shut off, and doesnt restart. when usb is plugged, it reboot and everything is fine.

someone found what is the prob? how i can make my damn pad reboot by itself without usb plugged in

Thanks