Upgraded PC and performed a clean install of Windows 10, and now my activation key won't work.

[SovietRussia]

Is there any way to get past this or do I need to hand Microsoft another $100 for a new key?

Details: upgraded PC from an AMD build to Intel/Nvidia, so I figured I'd format both my drives and reinstall Windows. Day 1 goes fine, but Day 2 I boot up and see that wretched Activate Windows shadow in the lower right corner of my screen. Dammit... how do I get rid of it? The activation key that came with my disk isn't working.

 

[USAFRet]

Is there any way to get past this or do I need to hand Microsoft another $100 for a new key?

Details: upgraded PC from an AMD build to Intel/Nvidia, so I figured I'd format both my drives and reinstall Windows. Day 1 goes fine, but Day 2 I boot up and see that wretched Activate Windows shadow in the lower right corner of my screen. Dammit... how do I get rid of it? The activation key that came with my disk isn't working.

Is this the recent 1607 Anniversary release?
If so, see this: https://support.microsoft.com/en-au/help/20527/windows-10-activation-troubleshooter

 

[geofelt]

If your copy of windows 10 was originally OEM, it is tied to the original motherboard and you need a new license.
Possibly a phone activation will work if you built the original pc yourself. MS is lenient on this. (not so much with prebuilt)
Could not hurt to try.

 

[manv]

Your Windows 10 key is tied to your hardware so any major changes to the hardware can cause MS to think it is a different system hence prevent you from using the key you own.
Try to get help from MS themselves.
But pretty much you made yourself a new PC(except the HDD) so I don't think MS will let you use the old key.