Hi I have account with adsense and place they ad units on multiple sites. I created the channels and can sort of see how much each site has clicks and how much it pays.

One of the sites, even though it still has the sam traffic stopped bringing revenue. The ads are still showing though

Is it possible that Google Adsense can block one site only rather than the whole account. Can this be checked?

I think, Adsense blocks the whole account, if they suspect you did something against their ad publishing policies.