on start up, go to setup and see if you can start it in safe-mode, that way you might get to trouble shoot it, if not, call a PC repair guy.
Does the computer continue to stay on ? and only the monitor is malfunctioning ? ok from what you wrote yes only the monitor is not working . Do you have access to another monitor ? a friend with one ? I hope that one is under warranty . the fact you're getting the brand logo means you are connected to power .
is a gray screen the normal color ? Ok when in doubt . Ok go behind the computer and trace the cable from the monitor ok there are 2 screws usually you're able to undo by hand , see if its loose if not undo entirely and then reassemble . hopefully this has an positive affect if not a repair shop is the best option
that's tough to nail down . I think your best bet is a shop emily and come back and tell us what was the problem
Is that after the windows logo? I may be able to help
Right When the computer boots up try pressing f8 repeatedly til you get a menu. If this works, go to safe mode and see if that works.
Would need more information to even begin to help. laptop or desktop? for starters.
get a new lap top....or...go to computer doctor....