Thanks for the reply,
The BSOD only appears when we are trying to use the usb to serial port converter. At all other times the laptop is stable and happy.
Running the built in memory tests and chkdsk is no problem, but the machien being a laptop makes more invasive troubleshooting techniques difficult.
I guess we should try the convertor (Usb2serial) in differnet usb ports? and maybe on a second laptop to try to establish whether it is some laptop component or the convertor (which seems most likely)
The only real option to do that though is another laptop which is the same make, model and age with the one experiencing the problem. If there is a laptop component fault how likley is it to have the same fault in the two items of the same make and model?
Thanks for your help and any thoughts!