So problem was in chair not in computer (PICNIC)  although the driver was (and still is) reporting an error. Didn’t even realise the camera had a privacy cover which had inadvertently slipped over! DOH!!!! Thanks fir your help anyway 
Made the mistake of upgrading to Windows 11 and now my integrated webcam does not work. Updated all drivers, deinstalled and reinstalled with no joy.  Device Manager says its working fine but the details show this error Device USB\VID_0BDA&PID_5538&MI_00\6&88b1a1&0&0000 requires further installation. Contacted MS who tell me its a Dell driver although Support Assist tells me al my drivers are up to date.  Device details say its an MS driver version 10.0.22000.176 Have spent 4 hours this AM trying to resolve through all troubeshooting steps and got nowhere......  
Windows 11 and Inspiron 7400 Integrated Webcam