Quite a lot of people don't manage to boot into Safe Mode, even with a working keyboard. So that doesn't say enough.
- Can you get into the BIOS setup with this keyboard the usual way? Does the keyboard work there?
- Does a PS/2 keyboard work (if you can connect it)?
- If your PC has an optical disk: can you boot from a Linux disc (free to make) or your Windows Install disc (free to make) and does the keyboard work there?
- If you don't have an optical disk: can you boot from a bootable USB-stick (such as the Windows Recovery drive you made).

Finally, if it's just the USB on your motherboard that doesn't function any more, installing a USB PCI card might be the solution.