I've got the main router on the ground floor which connects vi wifi no problem, but two floors up I have a second router which shows a strong signal but won't connect saying the signal is too weak, up until two days a go it was working perfectly, could it be the firewall in the routers software stopping the connection, any help much appreciated.

The fire wall will block or allow a singal but not make it weak.  It is detected that the power level of a signal from the laptop or its own TX signal is weak.  If your connection monitor has a level detector in it like a cell phone does see if the signal from the router is weak how many bars show.  Under connection in window you should have some scale for wach signal it see.  Maybe its try to lock into down stairs when up stairs so it looks weak, maybe upstairs has no signal.

The fire wall will block or allow a singal but not make it weak.  It is detected that the power level of a signal from the laptop or its own TX signal is weak.  If your connection monitor has a level detector in it like a cell phone does see if the signal from the router is weak how many bars show.  Under connection in window you should have some scale for wach signal it see.  Maybe its try to lock into down stairs when up stairs so it looks weak, maybe upstairs has no signal.

OK thanks a lot I'll give it a try when AI get back home tomorrow.