If you have a Lenovo laptop with a flashing LED on the power switch but will not power up, we have the fix. This short video shows a quick disassembly of a Lenovo Flex 3 1430. You can then unplug the battery and solve the issue.
In theory, holding the power button down (5 seconds on a PC or laptop, OR 15 seconds on a tablet) will force the unit to power down. However, that does not always work and so you need to pull the battery.