all my open and closed activities are no longer showing in accounts page

all my open and closed activities are no longer showing in accounts page

Hi when i click into an account i normally scroll down and can see pages and pages of closed activities and open activities. Today they aren't showing anything, on each account page under 'closed activities' and 'open activities' it simply says 'no records found'.

Please help, i fear all my account historys have vanished!

Thanks
Nicki