i am using WordPress 3.6.1 and I have strange problem today. First I have to tell that my current website was copied from old website, both the WP files and database.

So in the current website, I try to install new plugin, but it returns error:

Downloading install package from <http://downloads.wordpress.org/plugin/xml-sitemap-xml-sitemapcouk.zip>…

Download failed. Could not open handle for fopen() to /home/k5841724/public\_html/wp-content/uploads/xml-sitemap-xml-sitemapcouk.tmp

Then all my plugins are dissapered (Akismet, Hello Dolly, etc), and I can't install any plugin. Nothing wrong with my permission, /wp-content, /wp-includes, /wpcontent/uploads all are set to 755. Any idea what is the solution for this issue? Thanks.

**addition note:**
all my plugins folder (Akismet, etc) still there inside wp-content/plugins folder, but not appear in WP Dashboard.