Studio 1558 didn't detect another display - screen OK - help please!

I have a Dell Studio 1558 running W10.  Had external monitor attached and working fine in extended screen mode.  Suddenly both the screens flicker and the Laptop can no longer detect any attached display.  When i try to detech additional monitors I get "Didn't detect another display"

I have swapped:

1) To another display

2) From VGA to HDMI outputs on PC, and swapped the individual cables.  Same problem

Checked Drivers and installation:

I have tried uninstalling and reinstalling drivers.  No effect.  Have rolled back windows and even reset windows.  No change.

The Display adapter properties says Monitor type "Generic PnP monitor"

Now Microsoft basic display driver says: Chip type unavailable, DAC type unavailable, Adapter string unavailable.  Total graphic memory 1978MB  (Shared system memory 1978MB.

UPDATE: (2 hrs later) 
The Device Manager now says that the chip is an ATI Mobility Radeon 4500.    The Device manager shows that that is installed.   The AMD Website says that for W10 the driver should be installed by Windows update.  The Device manager says that driver is version 22.19.128.0. 

The dell diagnostics say that the graphics are fine. 

I had came to the conclusion that the graphics ship has gone (but the laptop display is still working).   But I may be wrong as the diagnostics say that the graphics are OK and chip is clearly still there. Any body got any ideas

I am completely baffled.  Please help.

Have I missed anything here?  Any ideas for diagnosis and fixes? 

Thanks

Phil