Networking Win 7 and Xp pcs

Hi guys, i am just so annoyed of right nw. i installed a i5 pc as a server which has windows 7 pro 32bit @ a clients practice and there are 5 admin pc of which 1 of that 5 also has windows 7 pro and the 4 has windows xp pro. i had put in at other sites the same scenario and all works perfect just this current site i am unable to see there server from any pc and no pcs can see each other and the server cannot see any other pc. i installed new cabling yesterday thinking it could be a cable problem and still nothing. all firewalls are off networking sharing is on and network discovery. if i take the pc to my office and try on my network it works perfectly and i am able to access other pc and i can see other pcs. just onsite its doesnot work, its like i am about to fail here PLEASE HELP:(

<edited by moderator - etaf>