Down arrow key not working

[xXxTORNADOxXx]

My laptop's down arrow key stopped working after a restart. My laptop is an ASUS X550LD and all the other keys are working. Could someone tell me what can the problem be? Thanks in advance

 

[liquidpower]

try plunging in a external keyboard and let us know if the key works on that if not something software if yes maybe something hw

 

[xXxTORNADOxXx]

the usb keyboard works

 

[rgd1101]

MERGED QUESTION
Question from xXxTORNADOxXx : "laptop keyboard problem"

I have an ASUS X550LD laptop. After restarting my system some keys are changed. For example:
-If I press the F10 key the letter o is typed
-pressing the letter "L" will act as the right mouse button. I've tried resetting the bios, typing in a bootable cd and scanning my computer of viruses. None of these worked.
Thanks in advance!