The suggestion above about SATA drives didn't actually solve my problem, but it got me thinking along the right lines. Here's what I learned about this issue through the above answer and answers on other forums. It turns out to be a common problem: It is typically caused by missing drivers for devices that are connected to the computer. Devices may include: any kind of USB device (could even be mouse or keyboard), graphics cards, any kind of disk drive, other kinds of cards such as PCI or PCIe Firewire. If you have a SCSI card then definitely remove it. I had a Dell keyboard with with built in USB ports and a media player control. I swapped this for a simple, plain vanilla keyboard. I also previously swapped out the graphics card that came installed on the T3400 for an older NVidia Quadro card as a fix for adaptor compatibility with my SVGA older monitors.  When I searched on the NVIDIA site, I discovered that there was no Windows 7 Driver for my graphics card, so I bought the DVI-I adaptors that I needed for the original card and put it back. My problem turned out to be the graphics card. On other forums  I have seen people overcome the problem by removing ALL USB devices. If you have a USB mouse and keyboard, this might seem to be a problem. However, once you have initialised the windows 7 install procedure you can remove the mouse and keyboard. Each time the computer restarts it will beep and warn that no input devices are attached, but after a brief pause, it should resume with the installation procedure. In my case, the fancy USB keyboard was definitely an issue too. Removing it after initialising the install allowed the installation to proceed by two extra steps. I was cursing Microsoft out for this issue, but to be fair I was not able to run a windows 7 compatibility test on my computer. I bought it on ebay without an operating system. If I had been able to maybe it would have flagged the problem graphics card and composite USB keyboard device. Don't know if this will work, but if you can't figure out what your driver issue is, you may be able to run a hardware and periperhals compatibility test by doing a temporary install of Ubuntu and then connecting to the Net. I had no problem booting Ubuntu from a USB drive and connecting to the net.  It works beautifully first time without any of the usual Microsoft shenanigans. In my opinion Ubuntu is a vastly superior operating system with a far more pleasant user experience. My only reason for sticking with Microsoft is legacy software. Think it highly unlikely I will ever consider buying a new Microsoft system again. They lost the plot after XP. Good luck   
Can anyone help me? I'm attempting to do a clean install on a Dell Precision T3400 with Windows 7 64 Bit OEM, but cannot complete the sequence. It goes through the entire installation sequence, restarting a couple of times. It gets as far as commencing the "completing installation" sequence - making what I think this is the final reboot - and then hangs. I think what should come next is the bit where I enter information for first time use -  time, date, location - computer name etc. I never get this far though. I have not upgraded the BIOS. It was previously running Windows Vista - but the disk has been wiped - so not sure if I can update the BIOS in this state. One other thing - I have swapped the graphics card. The monitor works fine during the initial installation sequence. Any suggestions? Thanks very much for reading. 
Can't Complete Windows 7 OEM Install on Precision T3400