Moved pc on same network not working

I have a small LAN with three pc's. One is running Vista Home Premium, one is running XP Home SP2 and one is running XP Pro SP2. They were all working fine, then I moved the one with XP Pro SP2 to a a different room, but plugged it into the same hardwired network. Now it says ir is in the same workgroup (MSHOME) as the other two which still work, but the moved pc cannot see or access the other two and vise-versa. I am hooked up ti a fiber optics connection to the Internet, but as I said they were all working fine until I relocated the pc. Any ideas, I have tried everything and even restored the system to a prior state before its relocation. HELP!