DS15 com port RMC stopped responding

Hi Managers,

We have recently taken delivery of our first DS15.  It is at a remote site.
I got local IT to connect a crossover serial cable to the com1 port and a
Windows server I can connect to using remote desktop; using PowerTerm on
the windows server.

All worked OK for a day, I could access the SRM console and RMC.  But the
next day, half way through reading a man page, access over the com port
stopped.

I cannot even do the esc esc rmc sequence.

The DS15 has been powered down (power cable unplugged) and up again.  I
talked local IT through setting console to graphics, running rmc and typing
clear port, to see if it corrected situation.

The com cable has been unplugged and re-inserted at both ends.

Does anyone have any ideas why it no longer responds over the serial cable?
I appreciate any and all ideas.

TIA

Shaun