Network connection problems

I have two computers networked connected by a network hub, computer A can connect to computer be and also see computer b, but computer b can only see computer A but cant access it ... i can ping computers from both computers, i dont have firewall up and i have shared files on both computer ..

the error message i get on computer B whos trying to acces computer A is ..\\<computer name> is not accessible (The network path was not found)

Both computers have xp home on them