@Auss JB, as per @jayeff , consider your BIOS needs updating but I’m really curious. Are you sure it’s going into “hibernation” mode or “standby” mode and not powering off because:
a) your power supply isn’t providing proper power
b) your battery isn’t holding a charge.
c) your power connector on your laptop isn’t broken down?
Have you tried running a live CD linux distribution to see if it does the same thing?
Does it power off regardless of being used or not?
Does it power off or hibernate? (How do you know)
Have you tried to use Windows without the battery plugged in?
It is also possible your battery is going bad and the machine shuts down to avoid overcharging the battery.
Lastly, it could be your CPU overheating and you need to clean out the fins and/or change the thermal paste on the CPU/heatsink.