Does it matter which subnet/pxe rep it comes from?
Any way you can setup a port monitoring and use wireshark to sniff the packets?
Is there any special options in your dhcp server?
Connect a machine that is failing to pxe boot on a hub ( not a switch) connected to one of your switch ports. Also connect another machine that you have connected to the same hub and have it acting as your pxe rep.
Does the pc still fail to boot to pxe?
I've seen a few occassions where non-standard switch configurations have blocked the pxe sequence and putting a hub in the middle removes this from the pc to rep equation.
Mark Star - http://www.marxtar.com
Home of Power State Notifier & Wake-On-WAN for LANDesk
What Bios version are your working 745's on?
Do these 745's have a different NIC in them?
You do not have an allowed.txt on your PXErep do you?
It would be located on the root of the c: drive on the rep. If you do make sure that the machines MAC address in question are listed.
We have decided to just drop the image to the hard drive in another machine and put it back into the failing machine for now.
We don't have the time right now to find a hub and get all the sniffing stuff set up.
And again I can pug the cable into one 745 and it fails, take that same cable and plug it into another and it works.
We don't rally have any special settings in the dhcp server, although the subnet mask is 255.255.252.0 so we have about 1024 IP's in the subnet.
I don't think the NIC's are different, but you never know with Dell. I did provide the version numbers in the original post.
No allowed.txt on the drive.
What do you see in a packet capture?
Are we sending valid data and that hardware is not understanding it? Or are we sending something invalid. If it is only that one piece of hardware, and always only that one piece of hardware, then it is that machine, its PXE code in the BIOS is broke or some setting in the BIOS is making it appear that way. If it is any machine but happens randomly, then it may be the network or even the PXE rep itself having intermittant problems that would be difficult to track down.