Software update keeps bring up the same update every restart: iMac EFI Firmware 1.7

Question

After I update "iMac EFI Firmware 1.7" and then restart and run update the system is asking me to update the same software again. I have run the update via software update, via the terminal and also by downloading the update manually and then installing and restarting.
The computer runs very slow even with plain word documents.
I cannot reinstall from the disks that came with the computer because I get the yellow trriangle with the exclamation mark and the error message "this disk cannot be used to start up your computer."

Answer 1

Hello
from the apple down load page
Boot ROM or SMC Version Information: After iMac EFIupdate has successfully completed, your Boot ROM Version will be IM121.0047.B1D
what is you version ?
ask system profiler to answer
go to apple menu ->about thismac click more info button
material tag
show something like that
Informations matériel :
  Nom du modèle :          iMac
  Identifiant du modèle :          iMac9,1
  Nom du processeur :          Intel Core 2 Duo
  Vitesse du processeur :          2,66 GHz
  Nombre de processeurs :          1
  Nombre total de cœurs :          2
  Cache de niveau 2 :          6 Mo
  Mémoire :          2 Go
  Vitesse du bus :          1,07 GHz
  Version de la ROM de démarrage :          IM91.008D.B08 <- LOOK at THIS
  Version SMC (système) :          1.44f0
  Numéro de série (système) :          xxxxxxxxxx
  UUID du matériel :          xxxxx-xxxxx-xxxx-xxxxx-xxxx
HTH
Pierre