Is this just the laptop having issues ? It could be the adapter in the laptop weather it be an internal one or an external one. I'm really not sure what else to suggest other then viewing the log files on the router to see what ip addresses have accessed it. It's possible that someone has cracked your password and is raping your internet, but I've not known it to cause signal loss. See if someone you trust can pop round with a lappy, or a smart phone with wireless on it.