Hi,
A lot more information would be helpful. Are all the fans, power supply, CPU, ans if any, case fans working? Have you given it a good clean recently, use compressed air? Have you changes anything other than your power supply? Is the power supply powerful enough? Did this happen any time before the new power supply? What are you doing when it happens and will it happen every time?

Sounds like a BSOD- If you don't want to reinstall try using the recovery console on the XP boot disk and perform a chkdsk /p on the drive.

Boot to the windows setup disk as usual but press R to start the Recovery Console when the "Welcome to Setup" screen appears.
If you have a dual-boot or multiple-boot computer, select the installation that you must access from the Recovery Console.
When you are prompted, type the Administrator password. If the administrator password is blank, just press ENTER.
More Info>http://support.microsoft.com/kb/307654

to a brand new on i assume ,and why did you need to change the psu,what was the old one doing or not doing

Well the old power supply unit burn so I change a new one with the exact wattage. No different than the old one. usually it just unplug and plug in kind of thing. I done it before a number of time. This is the first time I come across this problem. Usually this thing happen only when I change motherboard. So it kind of strange to me. Beside I am kinda hardware guy but only ok on software. So appreciate to anyone who can help on the software i mean.

Does the pc boot through to starting windows or keep restarting before that. If it restarts when starting windows, follow sennetor's advise, but if it does not get to starting windows then it may be possible the power supply is not supplying enough wattage for the system (probably why the previous one burnt), try getting one with a higher wattage.

It boot to Safe mode, Last best known configuration, thats works, Normal Boot and so forth. I already check the PSU and it is of the same wattage but I will double check again to make sure. Thanks for all your help.

Hi,
I don't know where you are getting the information from the CPU for the power supply but it could very well be the problem,
1. The new power supply is faulty,
2. The new power supply and the old one are too small to run your PC.
It will not hurt to have a power supply higher than your PC needs but it is asking for trouble to have one smaller. Your PC will only take the power it needs and if there is not enough it will shut down or freeze.
As it is a new power supply, can you take it back and ask them to check it?
"It boot to Safe mode, Last best known configuration, thats works, Normal Boot and so forth.
Are you saying that you can get as far as the screen that offers you these choices and when you select one it will reboot?
I assume that if this is the case, there is no message or blue screen, it just reboots?
If this happens every time, then it will probably not be the power supply at fault. But if this is as far as you can ever get and sometimes not even close to here, then I would look at the power supply.
Therefore, if you rule out the power supply, I would be looking at a windows repair using your OS CD. If you are not sure how, there are lots of good sites on the net that will show you with photos how to do it.

I just noticed that you mentioned it boots to safe mode.

When you get in on safe mode turn off automatic restart on system failure.

Right click on my computer>select properties(windows+pausebreak shortcut)
select the advanced tab> under startup and recovery select settings then uncheck Automatically Restart.
Next time you boot normally you should see a Blue Screen error message which might help.

My Money's on the HAL error given your PSU history.
http://www.itneighbour.com/subsite/automatic.JPG

ok if you have a new mb this can be fixed with just buy getting a 300 wat power supply now how ever a bad ram can do that but known for blue screens to but i have seen reboots from bad ram or not the wright power supply also you may want to check for a worm virus in windows xp sp 1 and 2 was known to get this when updating from microsoft why never known but i hope this works i also so pcrepair cheap paypal payments only and phone support free shipping on all repairs ty paul