windows update/trustedinstaller.exe vista

i'm not sure if this is a problem but when i 1st got vista windows update would check for udates when my pc was started and though out the day but now it seems that its not checking at all
i also use to get updates for windows defender everyday but i have had any from the 12 dec
as i said im not sure if this is a problem or if its just me thinking it is
i haven't changed any of the start up comands for the turstedinstall.exe or anything in that for a fact so as u can tell i am well confused any advice on the matter would be kool
and thanks in advance