Hi, first sorry for my bad English. Recently my company did a network upgrading (changing several units of old unmanaged 100mbps switch to a new managed 1gbps one, and do a correct new backbone cabling to avoid looping coz old cabling is a total mess). Everything went fine for a while. Then suddenly a week ago we have some weird connection problem with all PC in LAN. All PC can ping any PC fine, but cant sharing with each other. If i restart the PC, then it can sharing for a while before the problem come again. I try to do \ip_num but it just give me error of not accessible etc, and then the PC will become crazy soon afterward (taskbar missing, system32 error, freeze etc) and had to restart.Just one evening few days ago the problem seems to be gone for a while, before it came back next day morning.All internet connection is fine.Is it something to do with switch looping? There about 150 PC using XP Pro SP2 and several server (Linux and 2003 server). No domain, just normal workgroup. Please help.