How does unplugging battery and RAM (then reconnecting) fix Acer "black screen of death"? [duplicate]

This happens if the capacitors on the board are overcharged; it's either a safety mechanism (to prevent overvolting, some motherboards do this) or simply a malfunction from the extra electricity. The act of attemping to power on the machine without a power source drains the capacitors, and voila - functioning laptop. There can be a lot of causes for this - static electricity, ambient humidity, unstable/dirty power source, problems with the battery, or even a problem with the motherboard itself. It shouldn't happen with any regularity unless there's a component problem, or alternatively you make your living doing belly slides on shag carpeting.

Note that this can happen, not just on laptops, but on desktop PCs as well. Beyond that, it can happen to pretty much any sufficiently sophisticated modern electronic device, in theory. Laptops are just especially susceptible due to their design, so it's generally the only place you see this behavior.

The problem is that the laptop has crashed. Typically, some piece of hardware gets into an inconsistent or locked-up state, usually the part of the motherboard chipset that controls power sequencing itself. Because the power sequencer runs off standby power (otherwise, you couldn't turn the computer on unless it was already on), simply turning the power off isn't enough.

Removing the battery would eventually solve the problem, as all power would eventually deplete. But the laptop was never designed to drop its standby power all the way to zero as that's not supposed to happen under any normal operating conditions. To force it, you have to try to power the laptop on. That will drain all residual power from everything but the circuity that sustains the CMOS clock and BIOS setup information, which will unfreeze the laptop.