media upload not working

Hi,

I have a brand new installation with default Theme and no Plugins activated. My problem is that trying to upload images under Media -> Add New does not work. I don’t get any error messages, not even an HTTP 500 error, the request simply does not finish.

I have read a lot of posts in this forum and tried all of the suggested solutions. Here is what I tried:

– Disable all plugins (not necessary in my case since it’s a new installation anyway)
– Switch to Twenty Eleven theme
– Upload folder under Settings -> Media is empty and should thus default to wp-content/uploads (I’ve also tried explicitly setting it to that directory without success)
– Set permissions of wp-content and wp-content/uploads to 777 and change owner to the user PHP is executed with (in my case www-data). However, I do not think that it is a permissions-related problem, because a simple script I created in the wp root directory that executes mkdir(‘wp-content/uploads’); succeeds and creates the folder.

I have decent experience in PHP programming, but this is the first time I work with WordPress, so I have no idea what could cause the problem. If you need any more information on my setup, please let me know. Any help is highly appreciated.
Thank you!