It's possible to retrieve them if they are still in your old Inbox (or other folder you know they are present).
First you need to download & install the free Macallan's Outlook Express Extraction (MOEE).
Next open MOEE & from your OE backup, drag & drop your Inbox.dbx file (or other .dbx folder you know they are present). Right-click in the MOEE program & select 'Extract All Messages'.
Open OE (the program in your present PC) & navigate to the folder where you extracted the MOEE messages to. Then drag & drop them into your present Inbox folder in the opened OE. G