Imac couldn't read external HD the second time. Might be gone. Got hope?

My iMac couldn’t read the HD the following day after I plugged it in. The HD contains pics uploaded from my friend’s non-imac laptop during a trip to Europe. Got the HD 10 months ago. In that 10 months, I moved house so the HD was moved around a bit, not to mention the Europe trip. And I didn’t use that HD at all after my Europe trip.