Hace 5 años: I think it's 5 years ago. Something happened in the past.
Desde hace 5 años: Desde = Since.
I started (or not) doing something in the past, but it's still happening (or not) I'm going to the cinema each week since 1999.Or I haven't seen her since last Friday. Depending on the context it could be used in spanish with other meanings. Sorry I write a little English