If you have more than 2 PCs you'll need a hub.
You normally connect PCs to hubs with straight through cables - not cross overs. I suppose you could use a connector to connect a cross over cable to another crossover cable, thus making one longer straight thru cable.
Sorry the suggestion about putting the PCs together with a replacement cross-over didn't work.
I hope reinstalling helps, but I've never had all of these problems networking ever.
Let us know how you get on.
On the "today" page of <a href="http://www.scan.co.uk" target="_blank">www.scan.co.uk</a> this weekend, they're selling 3 x NICs, a hub and 5 metre cables for 49 pounds. May be it's a shame you didn't go for this!
<a href="http://www.scan.co.uk/today.htm" target="_blank">http://www.scan.co.uk/today.htm</a>