Macbook cannot 'read' my external hardrive

Hello,

I have been a Mac user for the past year and i have been loving it.
About a year ago, i formatted my external hard drive to the mac format and it worked perfectly fine.
Recently, it stopped working and the computer doesn't seem to read the hard drive. When i plug it in, the light glows as if it is reading but the hard drive symbol never seems to appear on the desktop.

Any help would be appreciated!
Thanks