Usually fixed by turning off power supply and pulling the cable as well.
On what? The monitor or the computer? It may be necessary to do it on both. As Bones suggested, the monitor could be reverting back to some default input. But also, the graphics solution could be reverting back to some unsupported setting too and what may be happening is simply that the graphics solution and the monitor are no longer in sync. They need to reestablish "handshaking". Hence a total "cold" reboot. And by "cold" I mean shut down the computer and flip the master power switch on the back of the power supply (if your supply has one) to off (or “0”) or unplug the power supply from the wall for about 15 seconds. Then turn the master power switch to on (or “1”) or reconnect power and boot up and see what happens. By totally removing power, you remove the +5Vsb standby voltage all ATX Form Factor power supplies are required to supply whenever the power supply is plugged into the wall and (if applicable) the master power switch is set to on. This standby voltage is distributed throughout several points on the motherboard, including RAM for faster boots and the USB ports too. This also keeps alive several features, including “wake on keyboard” and “wake on mouse”, and the network interface for “Wake on LAN” commands. A cold reboot ensures any device settings that may be held by the standby voltage are released, then reset when power is restored.
I also emphatically second Rei's suggestion to put your computer on a "good" UPS with AVR. It is actually the AVR (automatic voltage regulation) that makes a "good" UPS so important and that feature alone may prevent many of your unexpected shutdowns if those power anomalies are just short fluctuations (as most are) instead of full outages. Typically, battery backup during a full outage is just a nice bonus feature.
When you say this problem is "usually fixed", I get the impression this is a common occurrence. All the more reason to get a "good" UPS. Note I keep saying "good" UPS with AVR. Like power supplies, there are cheap, good, and best. The best are very expensive at $400 or more, and not needed for most users. The cheap are just that, cheap and should be avoided. The ATX Form Factor standard requires all PSUs "hold" voltages for a mere 17ms (milliseconds) during abnormal power events. A "good" UPS can react easily within that time frame.
Note surge and spike protectors are little more than fancy and expensive extension cords as they do nothing for low voltage events like dips (opposite of spikes), sags (opposite of surges) or brownouts (long duration sags) - not to mention full power outages. And for
excessive surges and spikes, they simply shut off power (if working properly), crashing your computer - never good.
I have an APC 1500VA UPS on this system, and it supports my computer, all my network gear and "two" 24" monitors. It will easily run this system for 45 minutes should I lose power. If I quickly shut down my computer and turn off both monitors, it will keep my network alive for more than 4 hours. That means I can still access the Internet with my notebook or smartphone.
Last, you might want to get yourself a
AC Outlet Tester to ensure the wall outlet is properly wired
and grounded to Earth ground. I recommend one with a GFCI (ground fault circuit interrupt) indicator as it can be used to test bathroom and kitchen outlets (outlets near water) too. These testers can be found for your type and voltage outlet, foreign or domestic, (like
this one for the UK) at most home improvement stores, or even the electrical department at Wal-Mart. Use it to test all the outlets in the home and if a fault is shown, have it fixed by a qualified electrician.
