Mikrotik Hang Overload Bandwidth

Problem happen when too many client turn on their pc.
80 client only.

2 box mikrotik has changed. but still same problem.

Rb1100Ahx2 & CR12524G-1S

1st Setting:
1 Subnet, DHCP, PPPOE.

2nd Setting:
5 Subnet, 5 DHCP, PPPOE.

Both type of setting still have same problem.

My network extra setting should have:
1 Share Local Server (Network attach storage) share 200mbps of data mapping by 15 client.
1 DB server accest by same client.

Other clients only using the Internet.

Hope someone can help me solve the problem..

*Sorry for my English.