I'm not a total beginner when it comes to Excel, but the spreadsheet i have
just opened has linked cells, very simple stuff like: -

cell a13 =sum(a5:a11)

If i change any of the cells a5 to a11 the total in a13 does not update
unless i go to a13 push f2 and then return
This is the same between sheets of the same file, and other functions such
as: -

cell b13 =round(b2*4/17)

this won't update either unless i go to edit the cell then hit return.

Has anyone got any ideas?

Many thanks