Thanks to Royan and Pradeep at Dell my son’s laptop (inspiron M5030) has now been repaired out of warranty (suffered the same 7 beep failure 3 months out of warranty). System board replaced today and all seems fine. Impressed with response from Dell particularly after initial check had revealed some evidence of spillage (son had no recollection of this!) but replacement of the system board demonstrated that this was in fact the source of the problem. So glad I found this forum!