thanks to everyone for their interest.
I appear to be running only a 32 bit Ubuntu, I can download a 64 bit but doubt that it has any bearing on my system crashes.
On the good side, I have removed the MA311 wireless card and the system has been up for 5 hours now, no sign of any instability.
The question must be - is there a driver more suited to the MA311 card? If there is I can get it onto a memory stick and then onto the machine, how should I install it? Is this a kernel rebuild process? Scary stuff.
Rans6...