You seem a little confused about terminology.
POP means "Post Office Protocol" and is now in Version 3 so referred to as POP3. POP3 is the software which allows you to download your emails to your computer and store them there. (Just for completeness, IMAP is a protocol which also allows downloading your email but they are normally stored on the email IMAP server).
SMTP means "Send Mail Transfer Protocol" and is used to send mail from your computer to the smtp server.
Are you sure you have set up your pop3 settings correctly in your mail software program and your password is correct.
What email program are you using?
If your settings are correct are you sure you have a reliable and consistent internet connection.
Is your problem on a computer or a mobile phone.