Are you using Windows XP Professional? If yes, we can try using remote access to control your computer and re-enable everything.
If no, you have to hunt around for a serial port keyboard. I have to say that this kind of keyboards are really rare, so rare that I have no idea where to find them.

Note that serial ports have 2 rows of pins, instead of 3 rows which are for monitors. If you are able to get such a keyboard, plug it in. If the computer beeps or give you a warning that no keyboard is detected, I'm sorry to say that you have to reformat.
Try starting up and see if you can enter.
If yes, try this:
[*]Press Ctrl + Esc to activate the Start menu.
[*]Press R and a Run window would pop up. Type in services.msc. Hit Enter.
[*]Press Tab one time and you will see Alerter being highlighted.

Note this column to see see if you have reached Plug and Play.
[*]Press P until you reach Plug and Play. Hit the Enter key.

[*]Press Tab until you reach Startup Type. Use the up down arrows to change it to Automatic.
[*]Press Tab again and press S to get your USB ports activated.
[*]Press Tab again to go to the OK button. Hit the Enter key.
[*]Next, press U until you reach Universal Plug and Play Device Host. Hit the Enter key.

[*]Press Tab until you reach Startup Type and use the up down arrow keys to change it to Automatic.
[*]Press Tab again and press S to get the services started.
[*]Press Tab until you reach the OK button. Hit the Enter key.
[*]Press Alt + F4 to close it.
[*]Press Ctrl + Esc again.
[*]Select Shutdown and shut down the computer.
[*]Wait for about one minute and plug in your USB mouse and keyboard.
[*]Restart the computer and see if it works. If it doesn't, and you don't have Windows XP Professional, the only way I see is to reformat.