XPS 13 keyboard flashing, won't power on

Hi

I have an XPS 13 which has a weird problem.

Firstly, it won't power on.

When connected to AC power, the backlit keyboard flashes constantly.  Pressing and holding the power button then changes the backlit keyboard to a solid light, but, the laptop will not power on.

Battery replaced 12 months ago, battery taken out and re-seated.

Has anybody encountered this problem before and has fixed it?

Many thanks for your help.

Regards, Steven