wp-login.php produces blank page

I am aware there are loads of other posts with the same issue, but Ive looked at about 30 of them and tried most of the things they suggest. I am getting really desperate.

What happens is the front of the site and the wp-admin login form appears fine, but after I enter my username and password I just get directed to a blank page with a single . on it.

This occurred after updating my site to 3.5.2.

Thus far I have tried:

• Renaming the plugins directory to disable it
• Removing the widgets directory
• Renaming and removing my theme directory to default it to twentytwelve (didnt work – broke the site)
• Replaced the wp-admin directory with a freshly downloaded version
• Increased memory limit to 96M and 128M
• Activated DEBUG to check for errors (nothing but notices and warnings, no errors)

Any advice is greatly appreciated!