Vista reboots when putting Laptopo into sleep mode

[RAJJ]

Please help,

I have a HP NC6400 laptop at work,

Everytime you put it into sleep mode it reboots

Ive tried checking the power options as so may sites refer to them but i have no hibernate option

network cable unplugged same thing just reboots after screen going blank and showing some HDD activity

Please help :sa:

 

[RAJJ]

help