Sales invoices have disappeared

HI, I opened my desktop app today to find that all my sales invoices have disappeared.
They have all been paid, but they have just gone!
I can still see the receipts for customers, but the invoices with paid in full have just disappeared.
How can I get them back?

you need to provide more details.
what do you mean by sales invoices have disappeared? all of them or few?
did the problem occur after updating Manager? if so from which version did you update?
some screenshots can give more clarity.