Asus laptop - power on issues

I have an Asus laptop (N551VW-FW210T), coming up on 6 years old. Running Windows 10, and had a clean install a couple of years ago. Never given me any issues.

Recently started having problems powering on. Press the power button, which lights up. Nothing happens. Give it a few minutes - hard power off. Try again. Eventually (might be 2nd time, might be 6th, might be 20th), the Asus logo will come up, and Windows will load - and it'll work absolutely fine, as if it never had any issues at all, no warning messages or anything. Power pack always connected and power on. No battery low indicator lights or anything.

Any ideas? Any log files to check? Initial thought is motherboard/BIOS issue, rather than anything OS/software related?