Why are my formulas 0?

None of the cells I used in my formula are empty so I’m unsure why it is coming up with 0. It was previously working and then suddenly it’s not. When I go and click on previous calculations that are correct it will now change those to 0 too. If I, = a cell from another sheet (which doesn’t require a calculation) it still won’t work. However if I manually write something like 1+1 it will calculate.
This problem isn’t happening across the whole sheet, only in some rows.
I’ve tried googling and doing what was suggested but none of that has worked. I’ve checked calculations are on auto and reloaded the page.
Does anyone know how to fix this?
It also keeps adding trace arrows, not sure if this is related.

If I change to manual calculations it will come up with some crossed out and the little green triangle. I did find some answers on google about this but it doesn’t fix my issue.

I’ve tested on a completely different excel sheet and it is changing previous answer to 0 on there as well but same as the other sheet where it’s not every row.

I’m very new to excel so I don’t know if I’ve accidentally pressed something to cause this. This is practice for university.