my portable hdd is dead..
the reason is probably why it is ejected in proper procesure. though it is responsible for meXD.
it costed about 5000yen (discounted price!) . And it takes only a few months since i bought.
important:
1. you should not eject HDD before you push 'eject button' or shutdown your machine.
2. you should not use HDD in wrong way. for example) using PC with standing and hanging portable HDD from PC.
3. HDD must be stayed in stable place.
Bye.