Very slow website,no error in a log

I have a good quality server with good performance. Till now I don't had this kinde of problem. So,I have installed Plesk panel,four months ago. I develop an ecommerce project using Laravel framework. Yesterday I wanted to open my website,and it was slow. No have any error,benchmark gave me good results. Any idea what's going on? Maybe last updated of Ubuntu has something wrong? Even plesk panel it's not opening. My domain is : onlinemarketmalta.com

via Chebli Mohamed