Config VPN for remote access to internal servers

[KSKC_IT]

hi guys I am new to check point and are using Check Point 1500 Appliance for my company.
As everyone is working from home, my colleagues would like to access to internal servers remotely. 

I have tried to config it but not very successful.
Remote access is ON with the office mode setting like this.

I have use the AD server as the Authentication Servers and the simplified network diagram are as below:

I am able to connect to the firewall using the Checkpoint VPN at home, but unable to reach the internal network.
May I ask what else (like routing, policies) should I config so that I could reach the file server from my home through VPN?

[PhoneBoy]

What shows in the logs when you attempt to access something over the VPN?

[KSKC_IT]

i have also config the vpn to use the AD server(100.xxx.xxx.21) as Authentication Servers.
and i am able to log in the vpn client and obtain the 172.16.x.x ip 
I can ping the 100.xxx.xxx.21 and 100.xx.xx.27, but unable to resolve dns (ping failed).

so i guess the next step will be adding the dns to firewall dns?
or shall i add a rule that allow all traffic between 172.16.x.x and 100.x.x.x?

[G_W_Albrecht]

Did you follow 1500 Appliance Series R80.20.15 Locally Managed Administration Guide p.23ff for configuration ?