In most cases, when we replace the motherboard with or without a new processor in the computer the previously installed system will not boot – probably we will end with BSOD. After that most people will go and reinstall the previously installed operating system because they think there is no other option to resurrect the old one. Well, this is not true. Here I want to tell what steps (without getting to the very details) you must do to resurrect previously installed system.
But first let think why the old os cannot successfully boot on the new hardware. The problem lies in two places (or at least in one of them). First is the controller of the system disk – if the controller in the new motherboard comes from other vendor or is simply incompatible with the old controller (for examle the old one was Intel IDE and the new is VIA IDE), then the os does not have the right device driver for it and as the result it cannot access the hard drive during boot resulting in BSOD. The second lies in the processor architecture (but only if the new processor is from other vendor, for example the old one was from Intel and the new one comes from AMD).
To cope with the problem with device driver for disk controller you have to have a Live CD or bootable USB flash (with BartPE, VistaPE, etc.) in which you can access the system partition and the registry of the installed system. You will have then manually place the right driver for the new disk controller in the “%systemroot%\system32\drivers” folder and manually add or edit the registry to make the driver being loaded with the system (the drivers are being represented as services in the following registry key: HKLM\System\CurrentControlSet\Services).
When you will be fine with the driver for the hard disk controller, then you need to ensure that the IntelPPM service is disabled (in the registry the start value must be set to 4). Without disabling it, when the new processor comes not from Intel, you will end up with BSOD as well.
This is not a detailed explanation of what to do exactly but it shows the way you shall go if you don’t want to reinstall the whole operating system after changing your hardware like motherboard, disk controller or processor.