I'm running Aceshop (Opencart based Joomla component, v1.4.

Today has sprung up a fairly strange issue out of the blue. Customers on our site are seemingly not able to login, and the website does not appear to be remembering login details. I have tested this morning by resetting a customer login I have and after I have logged out and try to login again, my details are not remembered.
As you can imagine this is a fairly major issue (and surprised it's just come out of the blue). I've gone through login whilst looking at console and no errors are reported (I had wondered if it might be a javascript conflict). Does anyone have any ideas what could be causing this (website is www.stickerscape.co.uk).
New customers who have been registering on the site have also been saying that they've been unable to checkout their purchases as when they're going through checkout the payment method section fails to load. I wonder if this is connected - I had thought this could be a javascript conflict also but in my own testing I'm struggling to replicate the issue customers are having.
Any thoughts most welcome.
Regards
Mike