Try to use place holder, it probably will help, at least remove one possible gotcha.

SELECT * FROM users WHERE name = ? AND pass = ?
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Use the following syntax:

@row_ary = $dbh->selectrow_array("SELECT * FROM users WHERE name = ? A
+ND pass = ?", undef, @binding_values);
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Use $dbh->err() to tell you the exact database error.

if you want to see whether there is a row satify certain condition, just say,

SELECT 1 FROM users WHERE name = ? AND pass = ? #replace * with 1
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In your case, there is really no need to run the same query twice:

  if($dbh->selectrow_array("SELECT * FROM users WHERE name = $uname_q 
+AND pass = $pword_q")){
        ($userid) = $dbh->selectrow_array("SELECT userid FROM users WH
+ERE name = $uname_q AND pass=$pword_q");
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You said that after you comment out the first if and the else block, it complains about $userid. That is a good indication that your query probably failed, according to the document, an empty list will be retunred in that case.