Wifi connected but internet not working upstairs

Hi, I have a MPB early 2011 and I have talktalk internet. I have absolutely no problems with my wifi up until the last week. I can use the internet perfectly fine downstairs when I am in the living room (where the router is located) as I am typing this using it, however when I go upstairs i.e. to the bedroom directly above where the router is situated I am still connected to the internet at the wifi symbol is black however i lose internet connection and I am not able to use the internet at all. This is a new issue as before, I was able to use my MPB anywhere in the house without any problems.

I don't believe it's the router as my iPhone connects fine upstairs and we also have a MPB late 2013 and that works perfectly fine upstairs.

Any help would be appreciated to rectify this, could this be something in my settings? thanks!