This is now officially the topic of more than 100 threads.  Nearly all of them have the solution.  I know, because I've been posting it on most of them.  Did you read any of those?

I can get to the new uploader on one of my accounts, and it works fine.  But on the other (more important) account, I get only the old uploader and have the exact same problem as everyone else.  It occurs on multiple browsers (Chrome, Firefox, IE 32 and 64, with or without Flash, Silverlight, Extensions disabled, etc) on multiple PCs and I haven't made changes to any of them.  So it seems clear the problem is on YT's server end, but there's no indication that they know about this or are working on it.

Turns out it IS uploading but is not serving you the proper page for you to enter your settings.  Don't leave the page -- open up a new tab and go to Video Manager where you can watch the progress and edit details.

No indication that anyone at YT either knows or cares about this.