Old vista hard from Core2Duo system to i5 will not boot.

Got hold of a Dell Optiplex 790 PC with an i5 2400. It was running a fresh install of Win 7 perfectly.
Took the hard drive from my sons PC (Core2Duo Q6600) running Vista and installed it into the Dell. (replacing the Win 7 drive). The Dell will not boot from the Vista hard drive and loops at the Advanced Boot Options screen, regardless which mode is selected.

My son wants to keep the drive with Vista as it has all his Minecraft files and mods etc.

How can I get the Vista drive to boot in the Dell?

I'm obviously being naive. I did just that previously with this hard drive and it worked perfectly, albeit with a same socket mboard and another core2duo cpu.

Back it goes - many thanks!

You can adjust the OS to boot on different hardware using Paragon Adaptive Restore CD
freeware. Download and burn the ISO to CD using Windows Image Burner, boot it and point at the WIn7 installation. It will be ready to boot in seconds.

You'll need to reactivate Vista on the new hardware at Computer>Properties. If this is a retail Vista license then it should be no problem.

Thanks for that - it is a retail version of Vista. Ive lost the cd though with the product key. Is this needed?

You'd need the Vista Product Key to reactivate or reinstall.

If it will start on its old hardware you can audit the retail Product Key using Belarc Advisor.

I would confirm the key using a second keyfinder program like Magical Jellybean.

While booted into Vista make your Vista Repair disk in case it needs repairs later.

Thanks guys. Working fine back in the old box so will locate the key that way.
Again, many thanks to all.