STOP GIVING BAD ADVICE
YOU DO NOT NEED TO REBUILD THE OS WHEN YOU CHANGE A MOTHERBOARD
Go to device manager
Expand all tabs
UPDATE NOT REMOVE, all drivers that are for HDD Controllers, ATA Controllers, RAID Controllers, USB Devices, Northbridge, Southbridge. BASICALLY Anything that is not standard. Update all these drivers to a generic driver.
Take HDD out, slap in new PC,
Install drivers from m/b CD (you will need this as you wont have the NIC driver installed).