Unplug the system, remove the battery and hold the power button for 30 sec. Remove and reinstall the hard drive (service manual below).
If the drive isn't seen thereafter, it's toast - you'll need a new one.
If it is seen, power up again, press F12 and boot to the diagnostics. Run an extended diagnostic on the drive - if the drive passes, see if Windows will boot. If not, proceed to replace the drive as above.