Numlock is something that should be always on. I don’t understand why it is often off at start up. If that is the case for your system, this page will help you to turn on the Numlock as system start up in Linux.
There is an option in BIOS that lets you set the status of Numlock at start up. You will have to search around for this one – it is located in different places in different BIOS versions. Make sure that it is on.
If the BIOS trick did not solve the issue, KDE has a configuration option where this can be set. That’s why I love KDE – whatever you want, there is an option for that…
Control Panel -> Peripherals -> Keyboards
It you still have the problem, install the program called ‘numlockx‘. This will turn on the Numlock at start up.