RB951-2HnD cannot connect internet

RouterOS Beginner Basics
1

i have a RB951UI-2HnD which cannot connect to internet, cannot get DHCP IP assigned. if i set the IP manually then i can connect but only for a short period of time.
tried to reset the configuration and even netinstall but still the problem exist.

please help

2

Mask of wan ip should not overlap with mask of lan ip. Make sure that the isp does not use any kind of access restriction by subscription or by mac address.