Wait. You're trying to boot to the existing Vista OS already on the HDD from the installation with the previous MB? If you replaced the MB with a different make or model than what was on the system originally, that is probably the problem. When the original OS was installed, it set itself up based on what components it found on the old MB. Now that there is a new MB with all different components, it is confused. Hence the BSOD.
In that case, yes, your best hope is to clean install the OS with the new MB in place. I thought you were having trouble just getting into BIOS. I must have misunderstood you.
Windows Vista isn't like Win7. Win7 has a downloadable .ISO file you can use to burn a DVD that will be the same as an OEM copy. But if you do a search for something like "Windows Vista ISO files" you will come across a 3-set group of files that will allow you to install Vista on a HDD. As far as using the product key to activate it, I'm not sure. Never done that with Vista. Here's an example if you want to try the download path:
http://downloadsnfix.blogspot.com/2012/08/microsoft-windows-vista-official-iso.html
The other way would be to search out a copy of Vista on ebay. I don't think you can find Vista still sold new anywhere. Good luck.
http://www.ebay.com/sch/Operating-Systems-/11226/i.html?_from=R40&_nkw=windows+vista