Site rank decreased in search resluts SERPs

Once you had a site hitting top search results?
Now it is falling in SERPs?
search your fault among the following :

1- Pop-up advertising, after your site come up, you may find pop-up advertising effective in generating revenue, but it may cost a lot.
2- Copied content , no genuine content.
3- Errors in sitemap, very common.
4- Your site might be hacked?
5- your site is slow, many images or high code/text ratio.
6- links for you are removed from sites linking to you.
7- bad content : serials, cracks, music, movies downloads ... all goes down.