Hi ad,
I tried to search your website on google and looks like your website doesn't have have problem with google crawl. See attachment.
Regarding the
webcache.googleusercontent.com/search?q=...p://www.dealsbook.de, google actually still caches your website (click the Text Only version on the top right, then the contents will be displayed) but I'm not sure why the page cache is visually blank.
Can you ask your friend why he was thinking the javascript on the head is reason of the problem?