Attack with no action, opponent passes with no action, can i still play an action

No — once you pass and your opponent passes consecutively without either of you playing anything, the Showdown closes and combat proceeds straight to the Combat Damage Step. Neither player gets priority again at that point (Rule 348; FAQ #7747).

Your pass was your last opportunity. The only way you'd get another action is if your opponent did play something after you passed — then the chain would resolve and focus would come back to you, letting you start a new chain (FAQ #6544). Passing back-and-forth with nothing played doesn't loop; it ends the showdown.