From what I've found the issue has to do with the CMPXCHG16b instruction.
If the CMPXCHG16b instruction is not supported,
It seems you can't do an upgrade install of W10 x64, but you can do a clean install of W10 x64.
Here's a Google search for Socket 939 on Ten Forums if you want to read/research more:
https://www.google.com/search?as_q=&as_epq=socket+939&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=http%3A%2F%2Fwww.tenforums.com%2F&as_occt=any&safe=images&as_filetype=&as_rights=
How much RAM do you have ?
If it's less than 4 GB, i suggest using Windows 32 bit.
Is your "valid product key" a readable COA sticker ?
What i would do if i wanted W10 x64 with this hardware
Get the gatherosstate.exe file and save it to a flash stick.
The instructions for this are in the tutorial AddRAM gave you in post #6.
Make sure i can read the COA key.
That way i have 2 options for activating Win 10, the COA key or the gatherosstate, better safe than sorry.
Make a system backup image of the Win 7 partition/drive, save it to an external drive.
I use Macrium Reflect, and it works reliably for me, ymmv.
Remove my current HD with Win7 and replace it with a new/clean HD/SSD.
If you can't do that, then you would have to install Win 10 on your current HD/SSD.
I like having more options for recovery, that's why i use a "clean" HD/SSD when making changes like this.