I just installed a new Gigabyte GA-880GM-UD2H with a Phenom II 965 since my old mobo died. I have just the old SATA hard drive with W7 installed and a DVD with the HP Windows 7 upgrade CD. This is/was an HP pavillion and upgraded to W7 through the HP upgrade disc.
When I start up, POST goes OK. Then attempts to load Windows but stops at the circle of dots. Then goes into the options to restart Windows or repair. Repair finds nothing.
I then attached an old IDE drive with Windows XP and I could boot Win X in Safe mode.
I then attached a SATA drive from a laptop with W& and it booted into W7 and began to install drivers.
I set up the old HDD as an external drive, connected it to my laptop and it reads fine.
I have the HDD in SATA0, and DVD in SATA 1. CMOS indicates HDD is IDE Channel 2 master and DVD is IDE channel 3 master.
You have to do a fresh install as your current install will be configured for the previous board. An HP setup wants the HP machine it was married too. A new type of Board demands a fresh install especially as Win7 marries to the Hardware it is installed on. This is part of the anti piracy aspect of Win 7.
Windows does not like when you change hardware. If you dont need any files that are on that hard drive boot off of the w7 dvd and do a clean install. You may have to call Microsoft and let them know you had a motherboard falure if you have a problem with activation. If you need some files then back them up first.