You have a nasty conflict here! Does the keyboard work without the mouse connected? If so, suggest that you boot up without mouse and then remove the mouse through Device Manager (you'll be using the ALT key a lot here in combination with underlined ltters in the menu screens). Reconnect mouse and reboot and see if re-detection does it.
You don't say what your configuration and connections are but I am presuming that both Mouse and Keyboard are PS2 plug and sockets (in which case don't forget to shutdown before plugging and unplugging as PS2 is not hot-swappable). If you have a serial mouse, make sure that PS2 is not enabled in your BIOS (and vice versa). Might also be worth checking that your machine is not expecting connection via USB - although that might be a quicker (temporary) answer to your problem whilst you investigate. USB is not recommended as a permanent solution as the drivers won't load in safe mode if you have to use it - and you'll be as stuck as you are now!
Failing the above - supply us with your configuration, any recent changes or events that could have caused the problem, and precise symptoms that occur and when they occur. Then we can all head scratch on your behalf.