Mage::getResourceSingleton('core/cache') returns false

Mage::getResourceSingleton('core/cache') returns false

Im having this problem: Fatal error: Call to a member function
getAllOptions() on a non-object in
/home/detona/public_html/app/code/core/Mage/Core/Model/Cache.php on line
456
checking in this file I see that:
protected function _getResource()
{
return Mage::getResourceSingleton('core/cache');
}
returns false..
Checking in the internet I tryed:
1) I deleted the var/cache/ and var/session/
2) /app/etc/config.xml and local.xml are there, and it was working before
Any idea?