Why won't my Mac Upload anything?

I need help. I just got my Mac a while ago, and I don't know tons about Mac.

My computer has never had a problem with uploading anything before. It would always open the window (Finder?), I would select the file, and it would upload it. Today, it just stopped letting that window open. It will flash the window for a second, and then it would disappear. It's not hiding behind the safari window, nor is it in any of my spaces. I've tried restarting my computer, and resetting everything that I know to reset in Safari (pop up settings, cookies, cache, etc.).

Any ideas?

 

It won't upload anything to anywhere... pictures (to facebook, etc.), attachment files in my gmail, etc. The upload window just goes away, then doesn't even flash again the next time. It's almost like the window is still open, but I just can't see it.