My external hard drive was working fine until yesterday but now I can't even access it. The EHD is a Samsung HD401LJ. I have checked all connections and they are alright and when I click on eject the EHD is there. What has gone wrong?

I it in a USB case? If so what model is it.

The brand on the EHD is Zaapa although it shows up as Samsung when ejecting. It is connected via USB port. I have tried several data recovery programs and my data is there, but what went wrong?