Laptop starting problem

My Dell N4010 has given me excellent service for the past two years. Suddenly, since a few days ago, when turned on, it does not start but there is a light gray screen and a message pops up that says: 

Warning: The AC adapter plug cannot be determined. This will prevent optimal system performance. Please check AC adapter connection properly, remove AC adapter and plug-in it again.

Press F1 to continue
F2 to enter set up
F3 to enter Boot menu

I checked the AC adapter but there is no problem with it. So, every time now I start my laptop, I have to press F1 to get it started when the above message pops up. Apart from being inconvenient, it is also annoying. Can anybody knowledgeable guide me how to get rid of this unwanted issue?

Thank you.