sudo apt-get update does nothing. No error message and NO update

Hi,

I am using debian 7.10, and I have been using it for 2 years.

I remember that it updated and upgraded correctly last week, but when I did

apt-get update 2 days ago, it won't respond. It doesn't show any error message, but there is no response at all. It just gave me new prompt back without doing anything.

I have checked the sources.list, but it looks fine.

I would appreciate any help on this.

Thanks.