Disappearing emails and attachments

I am running Windows 2000 Pro with Outlook XP. I receive emails fine but when I reply to them, they disappear out of my inbox to a black hole. I also have attachments that are not showing up in the inbox but if I move them to another folder and then move them back to the inbox they show up. I have checked every setting I can find and can’t resolve both issues. Please help!

Thank you in advance