Sometimes Magento may give suddenly some errors while it seems there have been no changes to the system; one of the more common issues is the following:
pdo_mysql extension is not installed
this problem is solved easy by going to the main directory of your magento installation and add (or create) a php.ini file with the following content in it:
extension=pdo.so
extension=pdo_mysql.so
extension=pdo_sqlite.soSo if you have the above error message; try to see if the above helps; if not, please contact support and we will glad to take a look into your problem.
