It could be overheating, coule be a faulty or dying wire, your wireless card/antenna could be loose/faced the wrong way/not in all the way, it may be blocked by something such as a shut door or something, etc.
Try disconnecting and then reconnecting, then if that doesn't work, move the router. If that doesn't work, unplug it for about a minute or more and let everything cool down, then plug it back in and reconnect. That should do it.