login problem in xp professional.

I have NT server, DHCP, around 40 desktop with OS windows 98 and XP professional. The problem is that on some uncertain day XP pro clients cannot logon to the server it only says wait loading your profile for hours but do not proceed. This happens only with the 3 machines with XP PRO. 98 machines work fine. The solution I have today is to remove (the patch cord) the machine from the network and reconnect.
Can anybody help to solve this problem??