I'm guessing it's a motherboard issue if the BIOS won't load, unless it's a real bad heat issue, and the system's not cooling down enough before you try and reboot.
If you're concerned about heat issues, do the following things:
Pop down to Best Buy, or somewhere similar, and pick up some Dynex silver paste, or whatever's available.
Pop the cover off the CPU, and unscrew the heat sink (pay attention to the springy screws, there's two different sizes). Blow all the dust out of the little fins (you should do this every six months, anyhow). Spread a thin
layer of paste on the silicon square, and re-install the heat sink and cover.
Make sure your notebook is propped up at an angle for good airflow. (I use a spindle of CD's under each corner). See if that helps.
If not, it's probably the motherboard.