black animation render's ?

hi i had a file i was working on for about 2 months , i always rendered out of the viewport just would save copy of the rendered image , but then i did some basic animation to the scene and right before i hit render animation something fell on my keyboard i tried undo a couple of times and then i tried to render the animation as image seq, png format like i had before in different projects, except this time my images are all black ? i have no idea why. could someone shed some light on this problem please