I'm using MODX the first time and it all worked since yesterday. I didn't change anything and the dashboard and the package manager worked without any problems but since yesterday I couldn't see the dashboard itself, just the top navigation menu in the backend/admin manager and the left sidebar menu with the ressources, elements and file tabs. Besides this empty dashboard the package manager doesn't work too. It just shows the table headings like name, version, release etc. without a table body.
I think that maybe the MODX Rest API is broken? My package manager source was http://rest.modx.com/extras/ and it worked a few days ago. I also tried http://rest.modxcms.com/extras/ already but it doesn't work too (returns a 404).
I'm using MODX Revolution 2.2.6pl and I also didn't change anything on the server configuration, so allow_url_open and curl still is enabled in my PHP 5.2.9.
It sounds as though you are not able to connect to the MODX rest server. http://rest.modx.com/extras/ will not return anything in your browser. It is currently running. I have confirmed both on an external site and a localhost site and had no problem connecting to the server. You may be better served asking for help at the MODX forums