dialing another pc

i am having trouble dialing into pc at work. the pc i am dialing from is xp home…it gives me a error 678…i have another pc exactly the same with xp home on it in another location that will dial in no problems..these were both bought the same and setup the same…any suggestions on what i could try? i use the very same credentials on both…it is both local call..on the pc that does not work i have had a friend try it while i was at work and i can hear it handshaking trying to negotiate a connection for about 10 seconds then it quits and gives the error on the dialing pc error 678…please advise..
thanks