I purchased Microsoft Windows Professional 10 32-bit/64-bit All Languages Online Product Key 1 License from the dell website a few months back, but now I cannot find the product key, where do I look to find it?
If you already used it to activate a Win 10 Pro installation, the key is embedded on the motherboard and should be automatically recognized if you need to reinstall.
If you haven't already used it to activate Win 10 Pro, then you've lost it. Dell doesn't keep track of Windows product keys, even if they sold it to you. The PC might have a Win 10 Home key embedded on the board which would let you reinstall Home again.