HJ Fritz said:
My xp switched off without being prompted to. And now the external hard drive is not recognised.
You may have had a power sag or surge, or your PSU might be going bad. In any case, it sounds like it fried one or more components of your hard drive or it's enclosure. You can always try removing the drive from the enclosure and try attaching it directly to your motherboard or even in another enclosure.