ok say my opponet actvates snach steal and takes my monster then he tryes to attack and i actvate magic cylinder or negate attack can he still sac her for a monster after he tried to attack with her

and say i got a sworm of scrabs on the field can i flip him up and kill something then attack then flip back face down

1) Assuming your opponent has not Normal Summoned or Tribute Summoned that turn, then he/she can Tribute the monster equipped with "Snatch Steal" for a Tribute Summon.

2) Due to the effect of "Swarm of Scarabs", that is legal.