If you keep losing the wireless signal it looks like interference, or the routers on its way out. Routers normally have about a 3 year life span in my experience,
If it’s an older wireless G router try changing the channel, in most European countries you can only use 1-13, so allot of scope compared to some countries that have allot less channels available. Depending on the make of your router will depend on the exact process followed, but in general you login to your router via its IP address and go to the wireless settings and change the channel.
Heat can also be an issue for routers at the moment, check it’s well ventilated and not in a cupboard or draw.
If you are on a more modern wireless N router, most have auto channel. Some computers have difficulty using this, and testing for that can be a little bit of a nightmare if you do not know your way around device manager.
The easiest thing to do is wireless is bothering you, is get a wire. As long as you know a place that can do them cheap (£1 to 2 per meter is acceptable where I am from) measure the distance and bam, direct line.
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Its not down to the ISP if there are too many routers in the area. ISPs give you the connection to the modem, its your call to broadcast it wireless. If you do choose to get a new router, go for a wireless N draft and use it on 150mbps. The technology was made to be used in a highly used wireless enviroment.
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i would also like to add if he lives in the basement, you can normally only get 1 ISP per telephone line. and 1 phone line account per house hold in some places so its not as simple as just getting another ISP