After all this could be a too small a power supply issue.
I've got rid of random Windows XPSP2 lock-ups by separating USB iFeel
mouse from Logitech wireless mouse/keyboard combo. However, I've
noticed yesterday that after shutting down the system, power up would
not post video. The system came on (fans, hdds and all the rest) but
no video post happened. I've had to pull the plug on power supply,
plug it back it and presto system is booting. I've reseated all the
components and power plugs. Running ASUS probe temperatures, voltages
and fans' rpm are all within reasonable limits.
I've used one of these on-line PSU calculators and turns out that I
need a minimum of 370W power supply; so after all this could be my PSU
under powering the system. Or is it something else according to you?

Regarding BIOS full screen logo for my motherboard. Why is it showing
two different P4 logos every time I boot. One with HT (for
HyperThreading) and one without it. I haven't changed anything in the
BIOS - HyperThreading is always enabled; yet I've noticed that P4
logos (with and without HT) appear in random manner.

One more question:
Was anyone successfuly with ASUS EZFlash (Alt+F2 while booting) and
CD-ROM with BIOS file on it. I've burned DOS compatible ISO image
onto CD-RW with Nero - with only one file in the compilation -
P4PE800-E.ROM but I get: "P4P800-E.ROM" File cannot be found! message
when I try to use EZFlash. My LS-120 floppy is not recognized by
EZFlash at all.

/Technik

Case: ASUS TA-231
PSU: Enermax Whisper 350W
M/B: ASUS P4P800-E Deluxe H/W rev.1.02 - latest .inf Intel chipset
drivers installed; latest Marvel Yukon onboard LAN drivers installed
CPU: Intel (Prescott) 3.0GHz (1MB cache) 800MHz FSB
RAM: 2x Apacer 512MB CL 2.5 (not!!!) PC-3200
HDD: WDC 160GB PATA, WDC 160GB SATAII (main Operating System disk),
2xMaxtor 80GB SATA as RAID 0
FDD: Mitsubisihi LS-120 EIDE floppy
Sound: Creative SB Live! 5.1 24-bit
Video: BFG 6600GT 128MB (nVidia) latest WHQL certified drivers from
nVidia's web site v77.77