By "it will not boot" do you mean that the HDD is not recognized or that it "blue screens" when you try to boot. If it blue screens (most likely problem) it is because the HAL is different from one machine to the next, XP is very hardware sensitive. What you have to do to correct this is do an XP overlay which will install the proper HAL for your new MOBO etc. To do this you boot your XP CD and choose to install XP (not the repair using the recovery console) You will then be given a choice of either installing a fresh copy of XP or reparing a previous version. Choose the repair, it will remove your old HAL and replace it with the new. That should solve it.