could this be something as simple as the battery needing replaced? when the problem occurs the laptop is always connected to an AC power supply. Usually, when it is charging and the battery power is low. it is a lithium battery.
i am not sure if it is the power supply though, because, as i said, it is usually on AC power when the fault happens.
Also, to further my problems, i recieved this message on one occasion where i restarted my laptop:
"system cmos checksum bad"
this is not good...?