Cant enter wifi password

[Fabbymonster]

Good morning all, new poster here and very grateful for any advice offered. I’ve replaced my 2015 21” iMac, so deleted the running system. During the reinstall, we had a power cut and so I was left with the file with a question mark on screen. When I start up now and hold down option r, I get the spinning globe and can use either the wireless mouse or keyboard arrow keys to select the correct network. I then need to enter the WiFi password. There’s a flashing cursor in the box but I can’t type anything in using the keyboard. I’ve tried connecting the keyboard with different data cables but still get the same issue. I’m wondering if anyone knows how to deal with this or if it’s catastrophic! Thanks in anticipation.