Missing Invoices after restore

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Hi All, 

We installed new computers in our very small business over the weekend and upgraded Sage at the same time. On Monday when I came in i noticed that the invoice list is missing any invoices after 2013. But by this point my colleagues had already started working processing new orders.

No other information appears to be missing, all the invoices were created from Sales Orders and all the Sales orders are still there in the list. Any invoices I have posted are showing on customer accounts. 

Does anyone know of any way that I can retrieve these missing invoices?

Thanks, 

Charlotte