Could not determine temp directory, please specify a cache_dir manually in magento

You have to open magento/lib/Zend/Cache/Backend/File.php
Change:

protected $_options = array(
        'cache_dir' => 'null',
to
protected $_options = array(
        'cache_dir' => 'tmp/',

Upload the changed File.php and create a folder, called “tmp”
The folder must be writable, so give it ‘777’