Strange Computer Start Up Problems

Dear Reader

I am experiencing some peculiar problems whilst attempting to boot up my PC.
(Vital system specs after description of problem) Allow me to apologize in advance for any confusion this description causes, and its length!.

When I 'cold boot' (I will use this term to mean the first boot of the day!)
my PC will complete all bios Checks and continue without a hitch to the Xp logo screen. Upon reaching the XP logo screen one of three inter-related problems will occur.

#1.The bar under the XP logo will complete a few circuits and then freeze forcing me to turn the computer off, If I reset the PC problem #2 (below) occurs .

#2. After completing bios checks my screen will go black before reaching the Xp logo screen. Immediately afterwards the monitor will click into standby mode. After a few seconds I get a warning beep from my bios, the beep goes something like this:
HI,LOW,HI,LOW - looped pattern repeats indefinitely (with the occasional stutter) until I turn the computer off again. If I reset the same problem will occur.

#3.As problem #2. except that the Pc will complete loading on the Xp logo screen, then, as the monitor momentarily goes blank before the blue Xp welcome message screen the monitor will flick to standby and I get the beeps once again.

After repeating this on - off process 4 to 5 times the PC will have booted successfully and I am able to use it as normal without any problems. At any point during these attempts I will experience one of the problems above, by the end of these attempts I will have experienced all of the problems in no particular order. The reason I used the term cold boot is that if for instance I use the computer for 3 hours in the morning, go out, come back after 2 hours and boot up again; there is an 80% likelihood that the PC will boot successfully on the first attempt.Strangely this 'warm boot' seems to improve matters. It is important to note that if I were to use the reset button at any stage the system would never successfully boot, that is to say that problem #2 would occur indefinitely. I actualy have to turn the PC on & off with the front panel power button in order to pass through successive boot ups.

I have tried a number of things but nothing resolved the problems:
Checking, Cleaning and Re-inserting all cable connections, Pci slots and memory. Disconnecting all non essential drives and devices. Cleaning CPU fan, heat sink and remounting the whole unit. Formating my windows partition
and updating all drivers. I haven't tried fiddling in the bios as I am not sure what exactly I am looking for!.

I would really appreciate any help and ideas as to what causes this problem and how to possibly fix it.

Thank you in anticipation

Ash

OS Name Microsoft Windows XP Professional
Version 5.1.2600 Service Pack 2 Build 2600
OS Manufacturer Microsoft Corporation
System Manufacturer INTELR
System Model AWRDACPI
System Type X86-based PC
Processor x86 Family 15 Model 0 Stepping 10 GenuineIntel ~1716 Mhz
BIOS Version/Date Award Software International, Inc. 6.00 PG,
SMBIOS Version 2.2
Total Physical Memory 512.00 MB
Available Physical Memory 176.39 MB
Total Virtual Memory 2.00 GB
Available Virtual Memory 1.96 GB
Page File Space 1.22 GB
Graphics Card NVIDIA FX5500 128mb