my guinea pig only eats hay and not normal guinea pig food...what do i do?

i just purchased my guinea pig 2 days ago and since i brought it home it has not touched it's food at all. It's only eating the hay or whatever kind of bedding that came with the cage. i'm not sure what to do exactly because this is the first guinea pig i've ever had so i have no experience with them.
HELP!!! PLEASE!!! thanks :]