HP laptop won't wake up

I have a laptop that is roughly 10 years old. I’ve replaced Windows Vista with Lubuntu and it works well for the most part. One odd thing is when/if the computer goes to sleep there is no way to wake it. Pressing any buttons including the power button will not revive it and a long press of power does not kill it. To revive it I need to kill it by unplugging power and removing the battery from the bottom, then power it up again.
Does anyone know whether there is a way to wake it up? I’ve disabled sleep mode for most circumstances, but if the battery gets very low it will sometimes go to sleep.

Some older computers have issues with Linux and sleep mode, you would have to go through logs in /var/log to find what the error is and see if there is a fix.

Take a look at the BIOS settings… See if it will let you change any of the sleep states/power management stuff. If it will, disable everything and have it managed via Linux.