Problems staying connected with WNDR3800

Hello!
Last week we purchased a Netgear WNDR3800. At first, everything was fine (using 2 laptops through wifi). When a 3rd laptop was added yesterday, the connection was lost. It stayed connected to the network, but there was no internet access. After resetting the router, the internet access was restored. However, this problem keeps occuring throughout the day after rebooting the router. The problem keeps occuring even if we keep the 3rd laptop shut down.

I tried switching the channel from automatic to a manual picked channel (5), this didn't resolve the problem.

Could anyone tell me what I could do to fix this?

Thanks!