Can you work out what caused my problem??

[jeallen01]

"Cost no more than a dead cheap part from the spares box!"

Amazing that exchanging one dead battery for another brought it back to life.

"dead cheap" was a "slight" misnomer - probably should have written "dirt cheap" . The replacement was a "new" one from my photo-batteries spares box, and measured 2.99V before I installed it on the m/b

BTW: if this m/c is a "throwback" design then HP has been building those until (at least?) very recently - it was built around 2016!

From my experiences with CMOS batteries, where batteries were dead/dead they would still boot but the CMOS settings would have reverted to default which was usually the date the CMOS was flashed, but then again I have never had an HP

My experience also.