My HDD doesn't show only in my Imac

Hi guys,

I am having this problem, my external hdd doesn't show up on my mid 2011 imac 27" running osx lion mountain . the first time I tried to connect it accepted , but now i doesn't show up!!!!
the strange thing is that when i connect it to my mac book pro running lion mountain too it shows up and works perfect, and on windows it does too. i have tried other external hdd they work fine, i think it has something to do with the capacity, cause the other ones i've tried on the Imac aren't that big, 120gb , 320gb but the one that doesn't work is 1Tb.

Hoppe you guys can help me.
Thanks For all.

Size doesn't matter (hee hee)...how are you unmounting this drive?
Run Disk Utility and see if it shows up there. If so do a verify and repair.

yeah it doesn't show up in disk utility , but in other computers it works fine.

Last time ( and ONLY time) it worked the power went down at my house, when I turned on the iMac it stopped working.

Thanks

Does anything else work in the USB port you're plugging the drive in? (it IS USB right? or Firewire?)