I tried to use the view key in the tool : http://xmr.llcoins.net/checktx.html
But it does not work, after pushing the button it states that it does not get a connection with moneroblocks
Anyone else this problem?
Yes, a couple of people reported it already. Unfortunately, it's up to the moneroblocks site to resolve the matter or to the author of the webpage (or anyone else, really) to change the service from which the site fetches block info.
Alternatively, you can use this block explorer to check any TX, as in the linked example. Just find it first and use the interface to input address and viewkey and it will show you the real output and the amount!