using sum not working on one sheet to add numbers from different page.

using sum not working on one sheet to add numbers from different page.

Hi. I was looking after any help what I'm doing wrong, 
One way what I found 
=070622.C35+080622.C35+090622.C35+100622.C35
Not working
=SUM(C35;070622.C35;080622.C35;100622.C35)
Unfortunately this also didn't add the numbers together.
Any idea please?