imac mid 2010 21" after installing new hdd no boot from usb flash and when press option key with R key shows globus on screen with offer to connect to internet after entering wifi login and password recieve with error apple.com/support -1007D No boot

if you have created a bootable installer with Sierra, press the "option" key on startup WITHOUT pressing the "R" key to boot from the installer.

as well, if you are using a wireless keyboard, connect it to the Mac with the USB charging cable (if it has one) or try a wired Mac or windows keyboard.

Try connecting the iMac directly to your router using an Ethernet cable.

If that doesn't work, then you need to create a viable High Sierra installer.

see > Create a bootable installer for macOS - Apple Support

in that case, please see if your Mac starts up to a question mark - Apple Support.

I think it's the "windows" key, but not entirely certain. it also could be the "alt" key. I would try the "windows" key first.

I just googled it. it is the "alt" key that acts as the Mac "option" key.