iMac late 2009 new ssd install
The Windows key is the command key by default. Unless you have a fancy programmable keyboard and have changed things, try holding the alt key which boots to the boot chooser just to be sure the keyboard and USB are functioning.

If you had a newer Mac, then you can try again with recovery or internet recovery:


https://support.apple.com/en-us/HT201314
What keyboards can reliably be used to start up recovery or diagnostics mode on a Mac mini?


In your case the 2009 iMac needs bootable media so you probably need to bring another Mac and target disk mode or create a bootable installer. The PC keyboard will work now that you know Windows key is Command and Alt is Option, but you’ll need bootable media to continue.