[CentOS] CentOS 5.5 hangs on Acer Veriton X498G

I have installed CentOS 5.5 (2.6.18-194.17.1.el5PAE) on a number of Acer 
Veriton X498G desktop computers.  They seem to randomly hang when nobody 
is logged in at the console, i.e. I notice a hanged computer but have 
not heard complaints about computers hanging while a user was at the 
keyboard.

The symptoms are:
	Blank screen.
	Power LED on.
	Network LED blinking.
	No response to keyboard or mouse.
	No response to ping.
	Arp request from computer on same subnet gets "incomplete" for MAC address.
	Cannot ssh into computer, "no route to host" error message.
	
The power management BIOS settings are set to default:
	ACPI aware OS			yes
	ACPI suspend mode		S3
	Deep power off mode		enabled
	Power on RTC alarm		disabled
	Power on PCIE devices		enabled
	Power on modem ring		enabled

lspci:
00:00.0 Host bridge: Intel Corporation Core Processor DRAM Controller 
(rev 12)
00:02.0 VGA compatible controller: Intel Corporation Core Processor 
Integrated Graphics Controller (rev 12)
00:16.0 Communication controller: Intel Corporation 5 Series/3400 Series 
Chipset HECI Controller (rev 06)
00:16.2 IDE interface: Intel Corporation 5 Series/3400 Series Chipset PT 
IDER Controller (rev 06)
00:16.3 Serial controller: Intel Corporation 5 Series/3400 Series 
Chipset KT Controller (rev 06)
00:19.0 Ethernet controller: Intel Corporation 82578DC Gigabit Network 
Connection (rev 06)
00:1a.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset 
USB2 Enhanced Host Controller (rev 06)
00:1b.0 Audio device: Intel Corporation 5 Series/3400 Series Chipset 
High Definition Audio (rev 06)
00:1d.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset 
USB2 Enhanced Host Controller (rev 06)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev a6)
00:1f.0 ISA bridge: Intel Corporation 5 Series Chipset LPC Interface 
Controller (rev 06)
00:1f.2 SATA controller: Intel Corporation 5 Series/3400 Series Chipset 
6 port SATA AHCI Controller (rev 06)
00:1f.3 SMBus: Intel Corporation 5 Series/3400 Series Chipset SMBus 
Controller (rev 06)

Has anyone else seen similar?