Jon Murray, The first thing I would check is the version of 2008. The T420 requires 2008 R2 SP1, is that the version you're working with? I would also make sure that the BIOS and drac are current as well. You can find the updates here -  BIOS - [URL] and here  Drac - [URL] You can update as well as install the OS via the Lifecycle Controller (F10) on startup. Let me know.
Hi, We have just bought a t420, but whenever we go to install Server 2008 on it, it bluescreens shortly after the windows splash screen,so we never get as far as installation. The error is a stop error of 0x0000007E and PSHED.dll.Has anyone else come across this before and solved it? Many thanks.
Poweredge T420 unable to install OS