Dell latitude e5440 won't start

I added a memory stick to my laptop but it never started again. When i power it up, the power led is turning on for 15 seconds (solid white light) and after is shuts, the battery lights in amber color for 2 seconds and then the computer shuts off.

I couldn't find this lightning sequence in the support so i removed the hdd, the dvd and even the ram and still the problem occures.

no need to say that i"ve inserted one memory stick at a time for any of the dimms and it wouldnt help

Thanks alot