audacity records only for 0.6 seconds

I am trying to use Audacity to record spoken word on a HP Laptop.
The programme starts normally.
The recording device is set to ALSA: HDA Intel: CONEXANT Analog (hw:0,0).
The playback device is set similarly
The input level monitor works.
When I press the record button I get a recording for about 0.6secs and then the blue waveform goes to a strait line despite the input level monitor continuing to be live.
I can play back the 0.6second clip but cannot make it longer

Tried running Audacity in Pulse Audio by starting it with padsp audacity in a terminal but same thing.

Have also downloaded the package audacity-dbg and reinstalled all three packages.

Any suggestions?
John