processor being the problem - "Unexpected Interrupt halting CPU0"
This might be actual damage to the processor or it might very well be simply that you have not cleaned it and it is overheating.
To check overheating open the case and point a floor fan into the case. The floor fan should provide adequate cooling even if the thermal paste between heat sink and processor has failed.
If it runs OK while using the floor fan for cooling then you need to clean all the dust and dirt out (use some cans of compressed air) and you should also add some fresh new thermal paste between processor and heat-sink.
If it doesn't make any difference then the probable problem is the processor itself.
My PC keeps restarting automatically at different stages of the booting sequence. It has been working fine for 3 years until now. I have not added any new hardware or software recently so I assume that whatever happened must be related to a hardware failure. I tried to run WinXP recovery console but the PC does not stay on long enough to finish any checks and reboots. It does not start in Safe Mode either. I also tried to boot with a single RAM stick at a time and run memory test, but it did not make any difference and the memory test crashed with the following message for each RAM: "Unexpected Interrupt halting CPU0" The hard disk is fine as I tested it on another machine and it is unlikely that the RAM sticks failed all at once. Any ideas how can I tell whihc device contributes to the failure? Any ideas please?
Intel 2 CPU 6600 @ 2.4GHz, 3x1Gb DDR2 RAM, 320 GB HDD, Nvidia GeForce8800 GTX running on P965 Neo chipset.
Operating System: Windows XP Pro SP3