Question [Q] Check for update button not working.

Hi all, i need a little help. I've just unrooted my galaxy s3, using stock rom 4.3. Everything has gone as it should and is now unrooted stock rom. But have noticed something unusual, in settings when i go to about device/software update/ and then press check for updates, nothing happens, it doesn't check for anything. I really don't know what the problem is, and i need to get it sorted as i'm a bit desperate for money and need to sell the phone quickly, but unfortunately nobodys going to be interested if it won't even check for updates.
Any help would be great.
Thanks in advance.