well do you get any error messages? you could try right clicking any My Computer icon or sybol and click manage. then click Disk Management. look at all your storage devices. on the right it should say Removable followed by the drive number. also look for the drive size to get an idea of which one it is.
if you find it you could right click it and click explore and you may get into it.
otherwise you could try changing the drive letter eg: (L:\) to (F:\). right click the disk and click 'Change Drive Letter And Paths' and change the disk letter there. BUT do not do this if you have installed programs on this harddrive. they may not work if you change the drive letter, if you allready changed it you can change it back and it should work again.
the last resort may may be to format the disk which will wipe all the data. but lets try and avoid it coming to that.