First verify it is an issue with WordPress install and not a caching issue on your machine. Log into your admin area and click on add new post and click the tab for HTML above the edit box. If nothing happens then there is most likely an issue. Also type some text into the text box if it is white there is an issue and here is where you start.
Make sure you have cleared you cache on your browser before proceeding and clear it regularly while working through this issue. Always use the F5 key for a refresh to force a fresh download from the site.
Start by placing this line:
define( ‘CONCATENATE_SCRIPTS', false );
Right before stop editing line in your wp-config.php file
If this does not work move to next item and that is replacing the WordPress Admin files with freshly downloaded ones from WordPress.org
And when this does not work notice one thing that is happening that you may have missed and that is how the page is not completely loading. Then look at the source code and scroll to the bottom and look for the error and when you find that which is this case was the ecommerce store and then fix it and all will be well in your world.
In this case I found it to be wp-ecommerce had broken for some reason due to WordPress update.