Can not login

[captcha]

SMF 2.0.17
  Newly installed website. Can not login, it always show incorrect username or password. Actually, the username and password are correct. These usernames and passwords are from my testing accounts. No any usernames and passwords can pass login.
  What's wrong with it? I have  cleared browser's visiting history ( including cookies) and turned off SMF server's caching.

[Sir Osis of Liver]

Can you register a new account and login with that?  Running any mods?

[captcha]

Can you register a new account and login with that?  Running any mods?

Thanks,
I uninstall all Mods, now it can login.