One of the computers on our network is having problems. When you switch it on it goes through the boot up and when it gets to the "applying security policy" stage it just hangs, then eventually it just restarts, then it continues in this loop. If we disconnect the ethernet cable from the network, the computer loads up fine, then we can plug the ethernet cable back in and it's ok. Can anyone help solve this very weird problem?

What type of network is the machine on and what machines is it interfacing with during boot ie servers? nosey aren't ya, readin me sig?

I think if this computer is part of the domain, then it faces some problem to communicate with AD domain server when booting up . A clean OS re-install on this computer should be able to solve this issue. Hope helps..

Here's how I'd troubleshoot this weird issue. 1: Check that patch cable. Replace it if possible. Then reboot. 2: If plugged into a network jack, have that jack checked for collions. Maybe its a bad punch down. A FLUKE network analyzer will come in handy here 3: Boot into safe mode, check your network settings. Make sure you have the correct DNS server in your TCP/IP settings. I'm assuming its only happening on one PC, so your DHCP server's DNS setting is probably correct. If your TCP/IP config is set to static, try making it DHCP and reboot. 4: Try another PC or laptop, see if that PC does same thing. If not, rebuild OS on the PC like above poster said. John Carr Network Analyst

PICOHAT is right. It sounds like the machine is not receiving its domain logon and group policy data correctly causing it to hang. this is why when you unplug it and it boots as a stand alone machine, it boots ok. it is a weird problem though. do other machines log on to the domain ok? try updating group policy and checking the AD settings are correct. -D- nosey aren't ya, readin me sig?