My site is down. LINODE and Prestashop pass the ball and nothing happens

Hi, I apologize in advance, but I use Google Translate.
"The problem is this: my site http://knijarnitsa.com does not recognize me at all. He says that such a user does not exist or that the password is wrong … So I can not log in to the administration and process any orders. No. I changed the password or the name and I'm sure of them. The forgotten password button doesn't work for a long time and maybe that's where the problem comes from. The site is on Prestashop. The site's creator died in an accident and he knew everything about it. I had access, but no longer … I would like you to give me access to the site with your help so that I can work! How can this happen? I am ready to answer all your questions! "
This was my first request for help from LINODE 2 weeks ago. There has been no result since then. Of course they are very kind, but I want to work! I want results!
Unfortunately, the story has a sequel - now, except that I can not enter the administration and my site is not working. I'm not a programmer and I don't understand anything, but I regularly pay what my hosting and Prestashop want, and I can't work. LINODE says that everything is ok with them, but there is no website … Prestashop just takes money and asks questions, and they don't do anything
I hope I was clear and that someone will be found to guide me on how to solve my problem!
Thanks!