Just fixed it. There is a multi-cable connector from the HDD, not the thick pink one, and it had come apart at a connector just inside the C15, and I could not see it because it was tucked behind other connectors, until I started pulling the cables around.

It now starts properly and the play controls work, so Bruce was quite correct about the battery.

Thanks for everyone's interest and help.

Ross.

Control:15, TwinStore 2GB*2, 500, Auralic Vega, Pass XA60.8 x2, B&W 802D, Stax lambda & SRM-T1S, Prime Headphone Amp., HiFiMan 500