First and foremost, decide whether the desktop PC is going to connect to the router by cable or "wirelessly". If by cable, disable/unplug the Wireless Network Adapter because it should only have one connection to the "network" and that is via the router. The laptops also have only one connection to the "network", which is "wirelessly". This connection to the router should support both Internet access and File/Printer sharing.
The most common reason for PCs not talking to one another is a firewall issue, so make sure that any firewall software is configured to allow access to the networked computers. As you appear to have been running the network adapters in "Ad Hoc" mode for file sharing, it is possible that they are using different IP addresses when used this way than when connecting in "Infrastructure" mode to the router. Possibly, the IP addresses allocated by the router are being blocked by the firewall.
<<< .But i cannot connect to the internet through the host machine,i have enabled connection sharing in favour of the wireless network but it wont work >>>
When using a router, you *MUST NOT* have Internet Connection Sharing enabled on any connection in any of the PCs. There is no "host" PC and there are no "client" PCs. All PCs connected to the router have an equal status in the network and get their internet access over the LAN from the router and quite independently from any other computer in the network.