My Shopify store dosn't work maybe crash?

Hi Guys,i have my Shopify store from 1 year,with good result,like 400 visit a day with the right advertise. I have not change the advertise but from days ago,the site reach like 100 visit a days,and people don't try to buy. Someone try,abandoned and then buy. I have received some emails by customer who said he would buy some product but can't for site problem. From my computer,smartphone all works good,but i think maybe from other's country not,maybe crash. Someone know how i can resolv or try do find some problem?