[alexuk]

This has had me tearing my hair out for weeks.

I have a duo with a realtek onboard that would work OK when connected to to a buffalo WHR-G54S or directly to VM's box. The house had a network cable going out, then into the left and back into the back room upstairs, trouble was one connector had been removed while plastering. I put in one female at that end and tried hooking it up but got no connection. This is not something I'd done before so I spent ages trying to make sure I lined up the ethernet wires correctly but all it appeared in order. Moved to the other connector upstairs (a male) and proceeded to put hook up a female there too (I had fems not males). The cable is now a patch cable (ie not a crossover).
Tried again, no result. Inspected the modem logs and could see the PC making DHCP calls and being offered IPs but not picking up offers. I tried fiddling with lots of things in the router but no result.

Not one to be discouraged so easily I tried running another long cable (this one the new one that comes with VM's self install) and the PC / onboard realtek would accept the request. PC runs Vista and Fedora Core 8 - both work.

The conclusion would be the house cable is broken somewhere. However if I hook up the laptop it actually works fine! So should I conclude the cable in the house suffers from signal degradation so badly that the PC cannot establish a connection (but a laptop can!)? I took care to cross the wires just at the very end but again that's not something I've ever done before. But even if so why do I see the correct DHCP requests in the logs? The realtek inbuilt BIOS tests reports the lan (when connected through the house cable) as being 100Mbit with a length of 28m: if the degradation was really bad should I not expect to get a read of >100m?

Obviously the solution is to run the PC upstairs with no wires but given all the time I've invested on this any help would be greatly appreciated!