vista home premium can't check update

Hi,

My OS haven't been able to check for new updates for the past 2 days at
neither manual or automatic ways.

When I click on check for updates nothing happens, the bar simple continue
to behave like is searching for updates. Even the windows defender is popping
up the error "the program can't check for definition updates".

Can anyone tell me what is going on??

Thanx
Bruno