5 macs in house but 1 keeps losing internet?

In the house at present: 3 macbook pros , 2 macbook's, Time Capsule, Netgear W/M Router and a PS3.

MB's have gmail accounts and MBP's have 2 accounts: gmail and our own from 1 & 1. BT provide line and our ISP is Firefly.

We are getting loss of internet connection on just one machine.

The only difference in all the machines, is that my husband and I have a business account with 1 & l - he has same settings as me except for name.

However he can loose access to the internet up to 10 times a day, for no apparent reason. I may loose access maybe once or twice a week.

Sometimes, my 1 & 1 outgoing ability is logged off and I just have to take it online again by putting in the password, however his is constantly showing as offline and when he does the same thing...it has no effect. Firefly confirm that all is running exactly as it should on the system from them to us. They can see us coming up no problem. 1&1 confirm that all the settings for email are correct.

So....in laymans terms please, where do I start to tackle this?