Help! Http error when trying to upload an image

Hello! I am having trouble uploading images, when i try uploading the message HTTP Error comes up. I’ve tried changing to the browser uploader and the Error message is this:
The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator and inform them of the time the error occurred, and the actions you performed just before the error. More information about this error may be available in the server error log.
I tried uploading pictures of different sizes and I have the same problem with all of them. Tried changing them from .jpg to .png and nothing happened. Please help me!!!
Last night I was able to upload with no problems, why is this happening now??

Thanks in advance!