Re: Help - Outlook express
Let me assume that no virus has affected your OE. So now, are you using POP or IMAP for fetching emails? If you were using IMAP, all of your mails should be on the server.
OE is a lightweight email client and it is very fragile to Trojan attacks. Other thing I could think of is that OE can not handle more than few thousand emails, hence stops showing some of them (may be some expert can correct me here).
About archiving, have you compressed the emails before? There should be a folder in your profile where OE stores all the emails in a compressed way. You might want to backup that folder and then save it somewhere else. Here is a guide about backing up and restoring the emails in OE.
http://www.freebits.co.uk/backoutlook.html
For future alternative email client, I can recommend Mozilla ThunderBird.