Network Print Makes PC Turn Off

I'm stumped! One of my PC’s shuts down whenever someone uses the network printer! I’m have a peer-to-peer home network with 3 PC's all running WinXP Home (SP2) and a Brother network ready printer, all wired to a Linksys WRT54G v3 router. The problem started 3-4 months ago and affects only one PC, an eMachines Celeron D340. When you send something to the Brother to print, the printer emits a long beep and the PC shuts off immediately, like someone pushed the power button.

Initially it was a random event with the PC shutting down occasionally. My efforts to find a solution over the weeks must have done something because now it shuts down 95% of the time in response to a print from any PC on the network. This morning I even discovered that the PC will shut down when I push the GO button on the Brother to wake it up.

The affected PC also has an HP Inkjet printer attached that is shared on the network and so far there has been no problem using it.

Steps taken to resolve the problem:
-Searched internet for similar questions/problems (not much luck)
-Removed dust build-up from mobo, cards and power supply (not much buildup).
-Monitored temp and voltage with Speed Fan under a variety of conditions.
Speedfan readings during a Sandra burn-in run:
temp = CPU 61o C max / avg ~53o , voltage: 3.26 / 5.02 / 11.54 (avg ~ 11.64)
-Swapped router ports with another PC as well as the printer.
-Swapped / replaced Ethernet cables.
-Virus scans with AVG & McAfee
-Spyware scans w Ad-Aware SE Personal, McAfee & Windows Defender
-Malware scan online via Microsoft
-Updated router firmware
-Updated printer firmware & drivers
-Removed old Lexmark printer programs – checked for removal of all pieces in startup, services, files & registry.
-Checked start-up apps and services (via msconfig) for threats/unusual programs or paths, disabled or removed extraneous stuff


OS (all PC’s below) Windows XP Home SP2 with all critical updates

Affected PC: eMachines T2984 (Intel® Celeron® D 340 Processor, Intel® 845GV chipset, 512MB PC 2700, Intel® Extreme Graphics 3D, 64MB Shared memory, AC '97 Audio, Intel® PRO 10/100Mbps built-in Ethernet)

Router: LinkSys WRT54G v3 (Firmware v4.21.1)

Network Printer: Brother 5250DX Laser Printer (Firmware v2.2.0, PCL Driver v3.16, Brother Software v2.0)

PC2: 2800Athlon XP, Biostar M7NCD Pro, 512MB RAM
PC3: Intel® Celeron® D 340 Processor, ABIT IS7-V2, 1GB RAM