Constant rebooting, help please!

Question

Constant rebooting, help please!
Since suddenly yesterday, my computer reboots itself always
during the Windows XP start-up, right before it should
display "Welcome" (Choose user profile) screen. This started
yesterday when I was just surfing the net and listening to
some mp3s, I hadn't installed anything new for a while.
Now I can't get the system running even in safe mode, nor does
System restore help. After the progress bar of Windows XP
Home Edition, the machine just beeps and reboots.
There seems to be no heat problem (specs below), because I
can get to the bios settings by pressing Del, and I can
browse them as long as I want.
I am pretty sure that there are no viruses, my McAfee
updates itself very often. I have a ZoneAlarm firewall to
protect agains hacking.
I've had some reboots earlier, maybe twice a week. This
began after I changed my processor to AMD Athlon XP 3000+.  
But now something made my setup completely unstable.
I know I don't have the latest bios drivers, the old ones
did not work (had to use System Restore to get the PC
running after installing them, but I didn't have a chance to
install the latest ones before this catastrophe happened).
Should I do a repair install of WinXP using the install cd?
What should I do, and what might be causing the problem? Any
help is greatly appreciated. Specs are below:
CPU:AMD Athlon XP 3000+
MOBO: KT4V
OS: WinXP Home
GC: ATI Radeon 9600
HD: Hitachi 120 Gb
RAM: 1024 DDR (2 x 512)
Power: Nexus NX3500 (350 W) - AC Input 115/230V - 10/5A, 60/50Hz
Heat:
CPU 51 C
System: 34 C
CPU Fan Speed: 3813 rpm
Volts:
VCore: 1,648 V
+5V: 4,975 V
+12V: 12,106 V
-12V: -11.743 V
-5V: -4,976
Battery: 3,360
+5 SB: 4,921
Frequency/Voltage Control:
Spread Spectrum disabled
CPU FSB 166 Mhz
CPU Ratio x12,5/x13
CPU Core 1,650
DDR Voltage Auto
Termination Vol Auto
AGP VOltage Auto

Answer 1

Hello.
You motherboard does not support an XP3000+ unless you have BIOS 1.8.
Do you have any BIOS updates? I recommend the latest one.
http://www.msi.com.tw/program/support/bios/bos/spt_bos_detail.php?UID=362&kind=1
====================================
"I know I don't have the latest bios drivers, the old ones
did not work (had to use System Restore to get the PC
running after installing them, but I didn't have a chance to
install the latest ones before this catastrophe happened)."
====================================
You mean CHIPSET drivers, VIA 4in1? BIOS is not part of OS  
The AMD XP3000+ CPU that you have, is it the 333Mhz FSB version or the 400Mhz FSB version?
You board does not support the 400Mhz FSB version.
You RAM, are they the same make and model
Are they both PC2700 or PC3200?
Have you tried 1 stick at a time?