Linksys Router - Internet Disconnects In Few Minutes

In one setup, we have fibre optic connection given by the ISP upto Distribution box inside the house where the fibre optic cable is connected to HUAWEI-ECHOLFIE HG865 terminal .From the RJ 45 port in that device , the ethernet cable goes to the DLINK 8 port switch. All the 8 ports are connected with ethernet cables to 8 rooms going concealed through the wall.

Our ISP person tested the connection by connecting one patch cable (from the DLINK SWITCH via the wall socket)to the WAN port of LINKSYS WRT300N wireless router and connecting other ethernet cable from the lan port of the router to the laptop ,setup the username ,password, encapsulation pppoe and configured the internet .found working. I tried to configure the wireless in the house by fixing LINKSYS access point in some rooms.

Here the problem started. I cannot fix the LINKSYS router inside the DB in front portion of the house since there is no space in that and cannot keep the linksys router outside also, So I kept the linksys router inside one room and tried by connecting cable from the wall socket to a 5 ports mini switch and from the mini switch I connected one cable to WAN PORT of the linksys router and one cable to linksys's lan port because I want to share the internet in all the rooms.