Hi,
My PC isn't booting into the windows XP Splash screen. It reaches just about that stage and reboots.
I updated the BIOS. Switched the RAM. Used other (known working) drives. Took out the sound card and all the others cards.
Still nothing

Regards

Have you made any changes to the system recently ?

Have you tried booting into Safe Mode and disabling the reboot on error setting.
Right click My Computer > Properties > Advanced Tab > Start up and recovery options > Uncheck Automatically restart option.

Once you can get back into Windows the first thing to do is ensure that ALL of your drivers and patches are FULLY updated.

Hey, tanx for your response. I've tried this same thing happens. I tried booting in safe mood, last known good, or booting normally, same things happens. System tried to boot, reaches that point for the XP splash screen, then reboots.. happens every time

A repair install maybe a better course of action.
Here's (http://www.microsoft.com/windowsxp/using/helpandsupport/learnmore/tips/doug92.mspx) the official Micro$oft way of doing a repair install,
And Here's (http://www.geekstogo.com/forum/index.php?showtopic=138) one with screen shots.

Its not a softare problem. Swap drives and the same thing is happenign with a kown working drive. Boiled down to the Memory cards, Mother board or the CPU.

I was going to say "corrupted hard drive" as this happened to my girlfriend's father just last week. But as you have tried another drive, there's that theory out the window :)

I'd take it to a repair shop if you have got it down to just those three. They should have spare parts so that they can try a little trial and error to get the right bit. You don't want to spend a load of money on a new CPU to find out it was really the motherboard and vice versa.

My friend had this problem a while ago. You can try booting into safe mode, but if not the only way to fix this is reformatting/reinstalling Windows.

Try to format and reinstall the window