Visual editor disabled on 3.3.1 fresh install

I have been using 3.2.1 up until last week, when I started a fresh 3.3.1 install on a new domain. Now I suddenly have a collection of bugs that I can’t solve:

1. The visual editor shows invisible text, white-on-white, that can only be made visible by Ctl-A to mark all text.
2. I lost the ability to embed an image in a page. The “upload/insert” button is shown but nothing happens and no pop-up appears. The upload works okay from the Media section but not while editing a page.
3. The visual editor does not show its toolbar of controls and options.
4. The editor is stuck on the HTML tab; I can’t switch to the visual editor tab.

Things I’ve tried

• worked through all the solutions suggested in ‘Troubleshooting WordPress 3.1 – Master List’
• recopied all original WordPress 3.3.1 files (this was a fresh install but hey it doesn’t hurt)
• deactivated and deleted all plugin files and folders
• switched to Twenty Ten (and then Twenty Eleven) theme
• went to Users > Your profile > Visual Editor and tried both settings for ‘Disable the visual editor when writing’
• cleared cache, cookies and history
• tried different browsers (firefox 10, chrome 17, internet explorer 9) on my main computer
• tried a different computer (firefox, chrome)
• visited http://www.mysite.com/wp-includes/js/tinymce/wp-tinymce.php and looked for PHP errors or warnings (none found)
• Added define( ‘CONCATENATE_SCRIPTS’, false ); near the top of wp-config.php. This seems to help — what does it do??? (And don’t just say that it stops concatenating scripts.)

I’ve searched the forums and found similar constellations of symptoms but nothing much recent, and only the slower non-concatenated scripts has had the slightest effect for me. But this is only masking a deeper problem.

Should I delete this project’s database and create a new one?

Now my client’s project is a week behind and 3.3.1 is still nearly dead in the water.

Windows Server 2003, Apache 2.2.1, PHP 5.3.8, MySQL 5.5.16