I think the failed_today is stored in cheat_failed table, so lets try with this modification:
$sql=$Db1->query("UPDATE user SET clicked_today=0, xclicked_today=0, ptphits_today=0, earned_today=0, ptra_clicks_today=0, emails_today=0, floodguard_today=0, ref_hits_unique=0, ref_hits_raw=0, clicksref=0, referral_earns_today=0");
$sql=$Db1->query("UPDATE cheat_failed SET failed_today=0");