Stuck 'a' key on Alienware m17x laptop

My 'a' key has suddenly stopped working properly on my Alienware m17x laptop.  It seems to be stuck on so when i restart the computer there is a loud beeping.  When it gets to my password screen it immediately starts filling with 'a's.  Then when i get logged on the 'a' key has stopped altogther.  I have checked for any physical debris and nothing has ever been spilled on it.  Other things I've tried was reinstalling the keyboard driver, using windows on screen keyboard (the 'a' key works clicking the 'a' with the mouse cursor), looking for any new conflicts in the device manager, using diagnostics, and rebooting in safe mode. My peripheral drivers and BIOS are all update and there has been no changes to the system recently. So i'm convinced it must be the keyboard itself - but the key moves smoothly up and down. 

The computer is almost three years old and runs windows 7 (64 bit) pro.

Any ideas?  Or do need to get a new keyboard?

Thanks