Formatting external harddrive that already has data

Duleo2jc

Honorable
Feb 2, 2013
3
0
10,510
I've used my toshiba external harddrive for a couple years and have important data stored on it, but now when I try to use it, a window pops up that says it needs formatted for it to be used. Will formatting it erase the data on it? How can I fix this?