ASUS motherboard won't boot/post, no video

Need some help finding possible solutions before I start RMAing good parts.
Problem: System and motherboard have power, but no boot or POST.

Symptoms: Started out OK. System worked for about 2-3 hours, and then went bad. Installed OS. Updated BIOS to ver. 0302. Installed and updated Marvell drivers, ASUS drivers (except AI utility), EVGA GTX 260 drivers, SB X-Fi drivers. Had 2 or 3 times during that period when monitor went black for a couple of seconds, then came back on. During one restart while installing drivers, system hung before boot: did not go to Express Gate SSD, fans running full speed, all 6 white LEDs and one blue LED on MB lighted, monitor has no signal, HD not spinning up. Reset button on MB and case do not work. Have to hold on/off button for 5 seconds to turn off.

Actions: Turned on/off multiple times – same result, no boot. Removed sound card, disconnected DVD optical drives, replaced HD with a new clean HD – same result. Reset CMOS several times by changing jumper from 1-2 to 2-3 and back, both with and without battery installed – same result. Removed video card: case fans ran a little slower when started without it, but still no spin up of HD (reinstalled HD with OS). Reinstalled video card, fans back up to full RPM, still no boot. Did not overclock. I have successfully built many low and higher-end systems over the years, but this is my first LGA 1366 build, and my first with an ASUS mobo. Unfortunately, I don’t have a lot of compatible spare parts lying around to replace each one to test.

BUILD SPECS:
MOBO: ASUS P6T Deluxe V2 LGA 1366 Intel X58 ATX
CPU: Intel Core i7 920 Nehalem 2.66GHz LGA 1366 130W
MEM: 3x CORSAIR XMS3 2GB 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
VIDCD: EVGA 896-P3-1257-AR GeForce GTX 260 Core 216 SC 896MB 448-bit GDDR3
PSU: CORSAIR CMPSU-750TX 750W ATX12V / EPS12V
HD: Western Digital Caviar Black WD1001FALS 1TB 7200 RPM 32MB Cache SATA
CPU COOL: Noctua NH-U12P SE1366 120mm SSO
SNDCD: Creative Sound Blaster X-Fi XtremeGamer 7.1 Channels 24-bit 96KHz PCI
OS: Microsoft Windows Vista Home Premium SP1 64-bit
OPTC DRV: Sony Optiarc AD-7220S
OPTC DRV: LITE-ON iHAS322-08
FAN: Scythe S-FLEX SFF21E 120mm
FAN: 2x Scythe S-FLEX SFF21D 120mm

Repair/diagnosis suggestions?

Thanks.

Try it with different RAM (ASUS is picky, one build didn't like OCZ). G.Skill seems to work fine tho, as does Geil.