renders are just black

for some odd reason my renders of a scene i’m working on are black, just black. just a few moments ago when i rendered it was all normal but now something has changed. can anybody think of a setting that would do this? i am using cycles render engine.
thank you.

lighting?

Lost materials for some reason.

BTW, I requently save and frequently make backups - load one if you do the same.

More information required as it could be numerous causes
Render settings ?
cpu or gpu renderings ?
CUDA or OpenCL ?
Graphics card ?
Screenshots ?
Blend file ?
etc etc etc

ahh… winter’s block was correct for some reason the hdri light image i was using in my preview renders was removed, thank you guys.

I had the same problem with 2.61. I haven’t done anything other than add a plane and a Suzanne and adding a gloss material to both. I’d help if I could, but I just don’t know what causes it.