The laptop is probably losing its IP address due to interference or because you've put it into Standby. Often when this happens, the router is unaware that the IP address has been lost and it doesn't renew it. You should be able to recover without having to reboot by going into the Network Connections folder, right clicking the Wireless Network Connection and selecting Repair. This will force a renewal of the IP address.
You might be able to improve the situation by (a) changing the Channel number you use with your wireless network and (b) allocating a fixed IP address to your Wireless Network Connection.