|What model Gateway laptop do have; and which OS is currently installed?|
Was there anything going on last time you had it running OK?
As it tries to boot up can you try getting into the boot-menu option - press F8 p, or on some systems tap F8 gently a few times after the initial splash screen, and the one where usually something like "press del(ete) to enter setup (or bios)" appears.
I'm not hopeful about the above - but no harm to see...?
And can you get into the bios (aka setup)? If you can, post back for a little more on that option... But don't go tweaking in there for now.
If you can get to the F8 boot-menu screen (as I say not too hopeful there though) try last known good config.
Another long shot... Remove all power, battery included. Press and hold the on/off button/switch for about 20seconds. Then release and restore battery and see if any imporovment?