Hi,
First, it is complicated that something suddenly stop working without any kind of modification.
If you have some blank pages, please check your PHP error log or activate the PHP error reporting in your Joomla configuration.
You should have a PHP error but the server hide it and display a blank page instead.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.