WordPress and ubuntu troubleshoot

Hey all,
I am having a problem in wordpress. I do not know whether the problem is from ubuntu or wordpress. I am using the theme twenty eleven and when i want to upload a header image i browse to the image using the GUI which is in twenty eleven and i select the image.It takes me to the next page where im supposed to crop the image but no image shows. if i press crop and publish . It takes me back a page and there is a radio button but no image is present beside it. If i choose it as the header no image will come. I tried fixing the problem but i end up rewening the site and i have to uninstall and install all over again .

Thank you for your time and help,

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