all resolved.. thx to all including Dell-Cares.. boot recovery undertaken with no screen activity so not sure if it worked!! and then a full power flush and restart with only one monitor and no peripherals (USB external drive etc.) 
Hi all sure its somewhere in the forum but could not locate so sorry if I missed it... Done a recent BIOS update via the Dell Comand Upadate and this all seemed to go well with the system rebooting itself and the firmware update then tiked through did not see it fail or where the % got to but it progressed for a while.. then a reboot at the end (presumed) has resulted in blank screens (have 3 connected) neither pick up a signal and left this overnight for 2 nights no completion or improvement.. Full power off (the 10+ second hold causes simple reboot)... There must be an issue or simple solution.. any help and guidance most welcome..  TIA..  BMJ
BIOS Update Precision 5820 - fails to boot