The laptop primarily shut down with a "no time or date set" error.  This had previously been rectified by putting a new battery and motherboard into the machine by Dell whilst under warranty. 

Went through windows repair options but windows seem to have lost all admin accounts on the machine. Attempted to rectify this by booting via USB to add an admin account with windows media previously supplied by Dell however it does not give USB boot as an option in the Bios and I can not add it.

This machine is driving me crazy.  Bios is up to date and reset to default, any idea how to enable USB boot so I can try and fix this.?