The reason it returns a count of zero is simple: there are no matching rows.
That could be because it's the wrong table, the wrong DB, or (most likely) that the parameter value doesn't exactly match the cell content.
Sop start with the debugger, and look at exactly what
contains, then compare that to the row you think you should match with. Unless they are identical it will not match, and zero rows will be returned.
But you shouldn't do it like that: Never store passwords in clear text - it is a major security risk. There is some information on how to do it here: Password Storage: How to do it.
] - the code is C~, but the principle is the same for PHP but even easier because this exists: PHP: password_hash - Manual
And remember: if you have any European Union users then GDPR applies and that means you need to handle passwords as sensitive data and store them in a safe and secure manner. Text is neither of those and the fines can be .... um ... outstanding. In December 2018 a German company received a relatively low fine of €20,000 for just that.