This is alnmost so stupid it's funny, but I'm at a dead loss and growing ever more frustrated here 
First off a basic overview of how my network is setup-
Cable Modem==> Router (WRT54GS, Tomato)==> Upstairs hub (5 ports, routes to bedrooms/ loft)==> Downstairs hub (5 ports, routes to consoles, PC etc)
I'm having riduculous issues with the connection to the downstairs hub. This connection has been working perfectly for 9 months, nothing changed anywhere. A few days ago (Can't give a precise date), I started seeing some packet loss from the PC; I put this down to a dodgy hub & accordingly picked up a replacement.
This afternoon I swapped out the downstairs hub & instantly killed all connection to the network. Accordingly, it ought to have been a simple case of replacing the original hub & looking elsewhere for the issues
Putting back in the original hub did absolutely nothing, so I then swapped the upstairs hub for the replacement. This still gave no connection downstairs. (All the appropriate lights are on, but nothing seems to be getting through)
Taking the laptop upstairs and using any one of the three hubs I have produces a perfect connection.
Taking the laptop and plugging into the cable running from the upstairs hub down again gives a perfect connection.
Using any hub downstairs produces a total connection failure.
I've tried the obvious and disconnected all other cables than the links between the hubs & the final connection to the laptop, but nothing happens.
Thoughts please
-Leezer-

First off a basic overview of how my network is setup-
Cable Modem==> Router (WRT54GS, Tomato)==> Upstairs hub (5 ports, routes to bedrooms/ loft)==> Downstairs hub (5 ports, routes to consoles, PC etc)
I'm having riduculous issues with the connection to the downstairs hub. This connection has been working perfectly for 9 months, nothing changed anywhere. A few days ago (Can't give a precise date), I started seeing some packet loss from the PC; I put this down to a dodgy hub & accordingly picked up a replacement.
This afternoon I swapped out the downstairs hub & instantly killed all connection to the network. Accordingly, it ought to have been a simple case of replacing the original hub & looking elsewhere for the issues

Taking the laptop upstairs and using any one of the three hubs I have produces a perfect connection.
Taking the laptop and plugging into the cable running from the upstairs hub down again gives a perfect connection.
Using any hub downstairs produces a total connection failure.
I've tried the obvious and disconnected all other cables than the links between the hubs & the final connection to the laptop, but nothing happens.
Thoughts please

-Leezer-