What was it? The router firmware was old. He too came back with everything else worked. A month later he was going to call in support but called me again to ask if I had any new ideas. Since the router firmware was still the old what it came with I explained it's the first thing I update. That fixed it for him.
For some folk they don't want to do this so they end up with support calls (costly) or a new router. I know folk that don't want to get into all this so I understand the reluctance.
After that I suggest checking WiFi channels on the router which again means the owner has to dive in and learn about their gear.
My husband's brand new laptop has this weird problem. During most of the day the internet works fine, but for a couple hours in the morning (between 5 am and 8 am) it shows a connection to the router but the internet doesn't work. Today as I was looking for answers online (with another computer), it suddenly started working again, even though I hadn't applied any changes. All other devices connect to the internet work fine during this time.. it's only this new laptop that has this issue, and it happens most mornings, only in the morning. I really don't know anything about computers, but this seems like an unusual issue to me. Any help would be appreciated.