Computer wont turn on, no action

[NOT ADMIN :P]

its booting from the wrong HDD drive or the cd drive.

can u get into the boot up menu?

f8?

disabel primary and secondary and others then select the hard drive with your OS on it and ONLY that one.

Save and reset. (f10?)

If all else fails flash ur BIOS **(WILL VOID UR PROCESSOR AND MBOARD WARRANTY)**

if that fails take out the battery on ur motherboard and leave it out.

Unplug the power b4 and press and hold ur power button wen the power is pulled out. (it wont do anything noticable) but you have removed all static electricity for ur case and components. now put ur power in boot up and with 1 drive selected it should boot up ok.

[patio]

Why would you suggest flashing a BIOS for an OS problem ? ?
This is not the first time your advice has been borderline...

The hardware has changed by putting in a new CPU.
Every version of Windows since Win2K is tied to the hardware it's installed on and will pitch a fit on major changes...you can't simply swap a MBoard or CPU and expect the system to boot properly.

Repair Install of XP  may work for you...i suggest reading it thru to get familiar with the procedure and printing out a reference copy before you start.
You will need an XP CD for this.