GPO conflic, GPo Corrupt, dont know what, but why all pc of my network suddently loosing connection with server (netlogon and sysvol)and cant get any share from server?

Hi, I posted several question and i tryed to solve as expert saying, but for time being, its seems all are fine, but its not.
Generally problem started in Server , suddently, all pc would lose connection with server, they will not get any share from server ,when this happen every thing fine like exchange,Internet.
but when this problem start, if any one try to connect my domain it will take at least 30 minutes to connect and after connect they will not get any share(sysvol and netlogon) even server itself., server event Id 1030,1054, I tryed everything. server runs well for 2 days, then 3rd day suddenly it will start again. so i initially suspect ,
windows 98 pc is giving trouble , in fact, when i connect particularly one windows 98 pc to the server, this problem starts. so what i did is, i shutdown all my windows 98 pc in my network, its only running windows xp and my server is windows 2003. i had problem with ntfrs( i solved this one)

now can any one tell me please, where is the problem likely ??
I went through many forums , many Kb ,
what i am suspecting, GPO is conflicting some how, but dont know how and where,
and some forums say, DNs is giving problem.
if any one can help me with trouble shooting GOP , DNs and AD
or help me to find out where is the problem,
i would be gratefully.