After changing battery, my system beeped once, the keyboard lights up but it doesn't boot

[tomtc01]

My device had been slightly playing up in that the cursor had stopped responding to the trackpad, so I thought perhaps the trackpad ribbon had worked loose and opened it up to check. It hadn't but whilst there I noticed that the battery was swollen, so I thought perhaps that was the cause. I bought a new battery and fitted it and the machine made a single beep, but then nothing. It doesn't boot, the keyboard light up for 10 secs or so then dims. Nothing else. Have tried the usual - power and volume down holding...Charged up for 24 hrs, no difference. No response at all.

Any ideas?

[tomtc01]

....Apologies, my spec has not appeared and I don't seem to be able to edit my post

This relates to a HP Elite X2 1012 G1. Windows 10 64