Have had the problem since I bought the machine. The number lock key will NOT stay on and must be reset if the machine is turned off or rebooted.?
Try this: Boot to the signin screen, hit your NumLock button once then click the ShutDown/Restart icon to restart the PC. This has worked for me in the past.
If that fails, look in your computer setup screen (F2 in he Dell screen part of booting) to see if there is an option there. Be careful if you are not familiar with the setup menus. Can cause some issues there you don't want.
This was a problem that has come and gone since I bought the machine 3 years ago. It was good for the last 6 months but then I had an unrelated problem with machine became unstable so I did a low level reload where all the M/S files were reloaded but my files weren't touched. Now I'm back to square one. I went into the BIOS and reset it to the default and it works now at least for a while.