Where Did All My C: Drive Gb Space Go? (please Help)?

For starters i have a old ( in computer years)
Dell Inspirion E1505 laptop, i just recently wiped it,
So with that said i start with 51 GB’s (which is low to begin with) and i have about 2-3 Gb’s of music worth and im trying to Download world of warcraft ( which i know is huge) and it’s telling me i don’t have enough GB space…So i went from 51 GB’s to 17.5 GB’s? where did it all go?!