Vostro 3500 boot issue (doesn't boot at all)

Hello all,

I've a problem booting my Vostro 3500: it doesn't boot at all. When I press the power button, it lights white and multimedia keys (play, stop, previous ...) start ligthing white from right to left, then to right again. I can hear some sound inside the laptop (¿fans or hd?) and that's all. After a few seconds the computer faints (switches off) completely. No Dell Splash Screen, no LED Error Codes (numeric keypad, caps lock, scroll lock ligths) and steady blank screen. No external devices are plugged to the laptop.

Things I've tried so far with no results:

 - all combinations of battery/power cord
 - removing memory modules and hard drive
 - connecting an external screen
 - booting with/without a cd in the optical drive

Any help would be highly appreciated.

Thanks in advance.