Yep, says 5V 700mA on the label.
Hmm. You might want to Google it just to double-check that the 700mA includes start-up current. It seems a little unlikely that it wouldn't respond in any way at all over just 0.1A, but I have no real idea if that might be the straw, the lack of which fails to get camel over the hump, if you'll pardon a little word-mangling.

Also, have you ever used a similarly "high" powered device on that USB port? If it's not putting out literally the full 900mA that "should be" available, it could be giving the drive just shy of the necessary start-up current - .15A/0.75W is cutting it pretty damned close... (And if you're not already using the shortest, heaviest-gauge USB cable you have, do so.)
ETA: If you happen to have a powered USB HD dock, try it in that. That should tell you at least whether it's a power issue or a firmware/protocol issue...