lan impossible

Hey guys I use a lot the lan in minecraft but today I play with the Lan and i can't access to the server lan.
with a computer window 7 java 32 bit I can see the server lan with A computer windows 8 java 64 bit but i can't enter in it.But if I want to use the lan with my computer windows 8 the other computer can't find the server lan.
Thx I 'm a french young gamer and I can't soeak english well