There are many way in the internet. But I think of this way.

You can disable the usb disk, and you can still use the keyboard.
來源: http://actychen.blogspot.com/2006/11/simple-method-to-disable-usb-disk-on.html

1.
find /lib/modules/-name "storage"

/lib/modules/2.6.9-34.ELsmp/kernel/drivers/usb/storage
/lib/modules/2.6.9-34.0.2.EL/kernel/drivers/usb/storage
/lib/modules/2.6.9-34.EL/kernel/drivers/usb/storage
/lib/modules/2.6.9-34.0.2.ELsmp/kernel/drivers/usb/storage

2.
you can change "usb-storage.ko" to another name in these folder

or delete "usb-storage.ko".
( or rm /lib/modules/`uname -r`/kernel/drivers/usb/storage)

If you restore "usb-storage.ko" , system will connect usb without reboot.

簡單的說就是找出 usb-storage.ko 這個檔案，更名或刪除就可以了