Did some more investigations into this today and found that it is indeed a debian problem. Mint8, Mint10 and pclos all run normally. But LMDE and now Debian Stable (that I replaced LMDE with) both freeze until I do something with networking. The easiest way to unfreeze it is to disable wireless from within the network manager applet, but killing network manager also works (as does "ifdown eth0" on debian stable, although it didn't on LMDE). The strange thing is that Network Manager applet has an X on the outside of it and has no network interfaces shown inside it, and when clicked on it claims that eth0 (the wired network) is "not managed". Well if NM applet is not managing it then what is? I don't have any other network manager installed.
I should say at this stage that it matters not a jot what I do with NetworkManager, I remain connected to the internet at all times even if I kill NM.
It is kind of ironic that with so many people screaming about not being able to connect to the internet with Linux I cant stop it connecting
I suppose I could blacklist the wireless driver or possibly disable wireless from the bios as this machine does not use a wireless connection, but I would really like to get to the bottom of what is happening here before I do that, it is like a little challenge! On the other hand, this machine is rarely used and when it is, it is usually just for experimentation purposes so it is not a big deal for me - don't strain your brains thinking up a solution for me, if the problem interests you then by all means give me some input, but this is not a high priority issue.
EDIT. I seem to have found a reasonable work round for it. I just selected "disable networking" in NM applet (this setting was preserved through one reboot at least) and it now starts and runs normally, including an internet connection. But HOW
There is only one instance of NetworkManager running and like I say it doesn't even matter if I kill that since it isn't controlling the networking anyway.
Fujitsu Lifebook AH532. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Lubuntu 13.10,Ubuntu12.10 (Unity), Mint16 (Cinnamon), Manjaro (Xfce).