If it's plugged into a USB port, the guy from maplins is correct, makes no difference if the jumpers at rear of the drive are on or not, you only need the jumpers to be on if you are plugging the drive into an IDE port on the motherboard.
Search for Computer Management on Windows 7, then once you have opened that, look for Disk Managment in the left hand panel, click on that
and it will show all the disks on youre system, if the drive is there, it may be that you need to assign a drive letter to it, to do this you right click on the drive, and look for 'change drive letter and paths' and follow on screen
instructions, you can also format the drive from there, suggest if you are going to format the drive, then use NTFS file format for using it in Windows 7.