can ping but not shown in workgroup

hi,

I am facing a very typical problem in one of our netwrk.

The network consist of 1 system wint Win2k Prof. & other 6 PCs with Win 98/95. Till yesterday the network was working fine. But today the win 2k pc can access the other PCs as well see them on its network places. But the Win98/95 PCs cannot see any PC on its Network Neighbourhood list. But they can ping each other as well as ping the Win 2K pc also. Win98/95 PC can access other PCs by searching the other PC but cannot access the Win 2K PC.

The tricky thing is that if I keep the Win 2K PC outside network i.e keep the PC off or plug out the network cable, all other PC are able to access each other and all PCs are listed in Network Neighbourhood. Moment I plug in the Win 2K PC into the network, the whole network stops working as described earlier. Another thing is that the mapped shared folder of Win 2K PC is accesible from Win 98/95 PC.

I tried all I can i.e changing protocol, cables, NIC but not to any avail. I scanned for virus with NAV 2005 but no virus was found. I know the whole problem is due to some virus but don't know which virus it is. Can any one help me out in this.

I know formatting the PC will solve the problem. But there is no gurantee that the problem will not resurface.

Please help me out

shiju :x