WD Harddrive not working or recognised? HELP

Hello,

I have had my 1 Tereabite WD External Harddrive for around 6 months now. Has been working fine for most the time. The other day, I tried to connect my Harddrive to my latop without any success. The only thing that comes up is the WD SmartWare(F:) and also it says the Local Drive (H:). However, the F drive only contains a small part of the harddrive, around 300 MB and the rest would usually be in the G Drive(my main harddrive - with all my data and files). When I try to add the hardware from Settings > Control Panel, it only recognises the F drive. It is as if my main G drive with all my data is not there any more but I have deleted anything or changed anything at all.
Can any one help or advise what I should do to get this fixed please?

Thanks

Dave