The heater is not blowing. The heat is working, just not blowing in my 1998 Pontiac Grand Prix

Sounds like a blown fuse - local the fuse box - there is a lettering telling ur what fuse goes to the heat - ac -- fan motor - etc - -
also you can test the fuses by getting a cheap test light from walmart - then test each fuse with the key on - - replace all bad ones with a like fuse - [ you should carry extras ] - -also take down the viin number - call the local dealer and ask if there are any open recalls - some recalls stay for the life of the vehicle

Probably the blower fuse has blown. Check and change.