why am I stuck in a loop

The problem is that the aready installed XP is
A. Thinks that it is still on the first mainboard.
B. It has no drivers, it has different memory and the video may not work with XP.
Can you boot to safe mode? Try hitting the F8 key after the bios screen gose by. You need to load the driver for that mainboard.
When it trys to load windows it is looking for drivers for the board and thinks it is installed on a new computer.
What happened to the first board can you reinstall it and move your files from the drive?
You may need to do an inplace reinstall and call MS to get a new PID.

the computer is not allowing me to boot up in any mode. and when i take a working HDD from another computer and put it in that computer, it still do the same thing.

If you want to get data off that rive you are going to have to remove it from that computer and attach it to another computer so you can read off the data.

The problem is occurring because you have changed the M'Board as the replacement M'Board has different drivers required for Windows to work properly so as the wrong drivers are loaded you [b]Can Not[/b] Start Windows. If the old M'Board still works you can reinstall that and remove all the drivers from the Device Manager and then shut down insert the replacement M'Board and reboot, then allow Windows to find the replacement drivers and install what's needed failing that you'll have to do an Inplace install by following the directions here

http://support.microsoft.com/kb/315341

Col

If the memory is only a pc133, then I suspect that the motherboard is not of recent enough manufacture to support WINXP.

The loop you are stuck in is, XP on that hard drive is set to reboot on error, rather than stop on the BSOD. As previously mentioned by in all the good answers, it's a drivers issue. The only time I've seen a similar issue you described, was a bad IDE device that was crapping out all the IDE devices (including the hard drive). Try unplugging everything from the motherboard, except a mouse, keyboard, video and floppy. Get a bootable floppy disk and see if it boots ok. Then add a device, once at a time, until the problem appears. In my experience, the bad device was an internal Zip drive. When I disconnected it, the hard drive I thought was bad came right up:) worth a try....

RAM of PC100 or PC133 is perfectly OK (don't mix the types however)

The loop you are in sounds like an auto restart on error, to stop this go to
Control Panel/System/Advanced/Startup and Recovery/Settings and clear the Automatically restart box. This should enable you to see the BSOD error message.

However that doesn't solve the problem causing the error.

First try booting to safe mode (F8 key when booting) and open a Command Prompt box - it's in Accessories and type

SFC /SCANNOW

to check your system files.

However it may be a driver issue, so try a non destructive "hot" reinstall of XP, see this link for details on how to do that:

http://tinyurl.com/hutg5

Do you still have the installation disk for XP place it in the CDRom turn off and turn on the computer letting the CD boot to Windows and allow it to complete till the final page where it says press "R" for Console go to the DOS prompt. type chkdsk /p after windows fixes itself up try again it should run this time. Dont forget to remove the disc

Good luck