It doesnt matter that its wireless or not, the router can still drop its connection which will mean no internet until its reconnected, mine does this but luckily only once or twice a week, still annoying though and never worked out why.

Im not saying this is the case with yours but it just sounds like your router dropping connection.

You could try resetting it by turning it off at the wall for 20seconds then back on, might have to wait 5mins for it to reconnect though.