My wordpress show 500 error

it used to be a running site http://www.naryn.kg
after sometime running we started to get 502 error on admin page (edit, post)
then server went to maintanance without warning us. i thought it was wordpress problem.
i deleted htaccess, then config.php, then sql base. uploaded by ftp new wordpress files, can access readme.html, but cannot access install.php, admin page, anything. base is new, files are new, no htaccess, new right config.php, and these dudes from hosting dont know what is the problem. pLEASE HELP ME.