Ridiculously slow?

[#1]

No, nothing like that on any of the computers.
We all connect wireless, but we are in a small flat so its not like any of us are further than 10m from the router for it to be a signal problem. We haven't tried wired, but obviously this isn't really an option for us as we don't want wires running all the way through the flat.
I'm just confused as to how this can suddenly come on as a problem after it has been working fine for weeks on end.

[#2]

It could very easily be a signal problem if a neighbour has started using wireless on the same channel number as you are using.
You need to start a process of elimination, if a test using a wired connection gives normal speeds you know where to look!