Hi Hamdi,
I don't think your schematic attached properly. I'm a little confused too by the last post saying you are using the ADS1242, but all your code is for the ADS1243.
It appears there is something wrong with your sign extension or the declaration is incorrect. 16777033 is very close to zero, but in the negative direction. Are you using a signed value? After looking at the declaration it appears that you are using unsigned 32 instead of signed 32.
Best regards,
Bob B