I have 1700 active user and 8mbps download with 1.5mbps up

Dear all have isp, i have 1700 active user when the number of user mor than 1000 and down link upto 6mbps my system downed please say me how i solve my problem, i use Mikrotik IDE memory ver 3.2 and use hotspot authentication on normal pc set dell optiplex cpu 3.2 dual core 1G Ram.

well firstly you have to troubleshoot, where is the problem [why system is downed].
You may start from connection monitor and keyboard or Null modem cable to your router and check the console output !