How i can stop form elements to display after authenticating.

Code:
<FORM METHOD="get" ACTION="<?php echo $PHP_SELF ?>">
enter username<input name="user" type="text"><br><br>
enter password<input name="pass" type="text"/><br><br>
<input type="submit" value="signin">
<input type="hidden" name="abc" value="abc">
</form>
e.g
I display this form, after submitting, the same page is displayed, but now form elements should not be displayed how i can manage this.