That is unusual. On the Pi, do any lights come on? There is a red and green LED in the corner of the main Pi board. The other basic question is whether the screen is on, or if the cable has cone loose. The Pi does not always scan the display port, so of the screen is not detected during the initial startup it may not be detected at all.
Beyond those things, the most likely cause is a corrupted/failed SD card. The SD card architecture is not particularly robust and it is too common for a card to fail in use on a Pi.