Can't find external drive after iMac sleeps and then comes back

my Book studio, every time my iMac goes to sleep and then comes back on, I can not find my book studio with out disconnecting the external drive usb from my computer and then putting the usb connector back in. How do I correct this problem.

I’m at a lost for words but it seem I found out what the problem was but I can’t beleave it. I was looking  through the forms and seen where someone suggusted to plug the unit into the wall instead of an extension cord  so I said what the **bleep** and tried it, and it worked. I hope it will work for anyone having a simuler program

I’m glad you saw that post.  Usually what you experienced happens with people put too many devices on one circuit (outlet) by plugging in multiple power strips.   I would still consider getting a surge protector for that drive, though.