It could be Monitor or video card or cable
Connect monitor to another PC,
Try different cable (also check if its not gotten loose, seat it good)
that eliminates monitor/cable for the video need more info as posted ^^
ordered replacement video card, would not let monitor start.
could not install video drivers since could not see monitor. played with the cords for the monitor and last resort swapped to back up desktop monitor is up and running .
now need to figure out if it is the monther board