error detected Your shopping cart is empty

Version 4 .7 2
Hi please can you help anyone
I have just changed provider and I also updated wordpress to the latest version
I am not a regular user and my knowledge is very limited
My site is not working and I am getting the error detected shopping cart is empty although the shopping trolly is/has items in they go missing when it goes to pay pal ?
I updated the vesion because the site seems to be running slow wish Id never bothered now!
Any help would be appreciated
regards Ray