Need a Networking Expert to fix minute network issues with our LAN and WLAN -- 2

This is Umaer from AlRabeh Pack. We are having an inhouse micro soft server. We are using it for the sake of microsoft dynamics. We are getting some connectivity issues all the time (LAN and WLAN). We have a cisco router and DLINK xStack DES-3552P switch. Need someone to fix this problem.