Boot-up: message PXE-E53 no boot filename recieved

Try going to http://www.3com.com/other/pdfs/legacy/en_US/trblshoot_ris.pdf and see if this helps.

8100 1.7G P4
256M PC800
40G ATA 100 Hard Drive
24X CDRW
16X DVD
Microsoft Natural Keyboard Pro
Logitech USB Mouse
Nvidia 64M GeForce 3
NEC MultiSync FE 950+ Monitor
Soundblaster Live
Klipsch ProMedia 4.1THX Speakers
Windows XP Pro
CyberPower UPS
HP 970 CSE Printer
Epson C80 Printer
Epson Perfection 1650 Scanner

In addition to Greenwoods advice, the other PXE error that you posted earlier and the one you are currently posting, will continue until you post more specific details. Your first post states that you put a new motherboard into your computer.
Did you put an identical Dell motherboard into your Dell computer? Or did you put a retail motherboard into your Dell and put all your existing Dell hardware on the new motherboard?
The PXE errors are specific to a PXE capable BIOS and PXE enabled NIC.
Boot into your BIOS and change your HDD to the first boot device.
Pamela

Here is more information about PXE.

PXE (Pre-boot eXecution Environment)
The Pre-boot eXecution Environment (PXE, but pronounced 'pixie') is part of Intel's open wired for management (WFM) specification that automates client management.

PXE is the component that allows a PC to boot remotely from an image stored on a server. This can be used to install operating systems and software on client machines without having to visit them. It's now common to find this option on disk imaging packages. Even if an OS is installed, PXE jumps in first and executes the image off the server.

PXE has a wake-on-Lan element in it that allows an administrator to remotely power a computer by sending a signal to the network card. For this to work, both the NIC and BIOS of the client machine have to support PXE.

Typically a PXE-enabled NIC is directly connected to the client motherboard so that it retains power even if the machine is turned off. The NIC sits on the network listening for a wake-up call from a management station - and then cycles the power of the computer.

Administration tasks can be setup in conjunction with automated tasks, such as backups. If the client machine is not turned on, then PXE will do this automatically without administrator intervention