External HD not being recognized

I'm running a Seagate Free Agent Go FW 250GB external HD to back my computer up. Only thing is it isn't being read by my Macbook Pro. The last time I was able to back up my computer was 30 JAN 2012. I'm connecting it to my computer via the two included USB cords which I know are work fine as I can tell power is reaching the drive as the lights are on. I've checked in Disk Utility and my drive doesn't show up their either. I'm running 10.7.5. Any assistance would be greatly appreciated.