Here you go:Rainbowtables
(you don't need the client, just learn for now)Online hash cracker
(this will do fine and uses rainbow tables in itself)
Free of charge
But the knowledge you get there should be a kick-start, nothing more. Use it to find something more valuable on Google, as all information is incomplete.
As for the cracking problem: did you copy the right hex and set JTR correctly, like not trying to use a MD5 algorithm on an NTLM hash (don't know if that's possible)? Haven't tried that though, so can't help you further on that. Incidentally some hashes won't easily be cracked by certain software (because of settings or code differences)...