OK . .  ignoring the "flatulance generator" for the time being  
 
have you tried a spare key if you have one ? (guess you would have tried that if you have though)
If not I would also suggest as Dbug says remove your power sounder from under drivers scuttle .
Possible fire risk, so remove & leave off ( as most do on here ) or get a new one . (see disconnection/removal in maintenance guide)
Then try key re-sync .  ( did re -sync operate correctly when you did it previously  . . . doors locking & un-locking etc.? )
If you have to take the key apart again  . .  be careful of the very small imobiliser chip that sits in the horseshoe part of the key .
If it  is loose & drops out as key is pulled apart  car will not start at all. And hard to find if dropped on the floor /carpet/driveway etc.
It would also help future diagnosis if you update your details with your omega model ,year & engine  
HTH       
