thanks aerobelly. Right, I did observe good static precautions, being in electronics design and proto building I have the necessary stuff, wrist straps, mains lead with only earth connection etc.
The machine boots up and stays up as long as the wireless network is not enabled. I don't have any applications that I can leave running to test everything stays good. I have run the Ubuntu memory test and it goes through the 6 Gb of ram repeatedly without error. As soon as I enable the wireless network it becomes unstable and reboots at irregular intervals, from a few seconds to 20 minutes. It has connected and downloaded a few (200+ !) updates for Ubuntu and I have got as far as getting Adobe X... mpeg player add-on for Firefox before the system re-booted.
The wireless card in the new system is a known working card pinched from an old, but still working, desktop machine.
This morning I swapped the wireless network cards between the new system and my Dell desktop, which I am using for this browsing session. This was fruitless as neither machine had the correct drivers for the cards so I have swapped them back.
in /var there is a "crash" directory with 3 files in. I'll search through them and dmesg to see what they reveal.
Thanks again,
Rans6... (very new to unix)