Verbatim 1TB External drive not recognised on boot

Hi I have windows 7 with a Verbatim 1TB external drive, the system is not recognising the external drive. When I switch it off and back on again it then recognises it and loads it in My Computer. I have another external USB drive which works just fine. This problem started after I formatted the PC and reinstalled windows 7. It worked fine before under the same OS. I tried another wire and plugged it into another port but still have the same problem. Anything else I can try/

Any help on this please? The drive works perfectly, but only after I switch it off and then back on when windows is already loaded. If it is on while windows starts up it doesnt get recognised.