Turn it on; if it's off, it's gone bad.
It depends on the problem. Could be corrected by going to Control Panel, Display Options and making the corrections. It may be because the monitor is going bad or a magnetic fied is interfering with the displayMaybe a setting on the monitor itself needs to be changed. It could be a bad cable connection. There's no one fix for everything. Not even just replacing the monitor because the monitor might not be the problem.
Could be a bad cable, or a bad graphics card. However, try the simple fix, first. Detach your monitor from the power source and the computer, reattach and then restart the computer. Sometimes the connection to the computer and/or power gets loose, so the computer doesn't "see" it.
When the computer is not processing anything at all. The computer light is on the monitor light is not but nothing is processing through the computer therefore no data is coming up on the monitor, not even the startup menu.
Check the cable running from your monitor to your computer. It could be disconnected, loose, or be a bad cable. If you decide it is not the cable then it could either be a bad monitor or a bad graphics card.
Depends on what kind of brand it is and also how you take care of it.
I hope you mean the monitor, because the only thing I can easily think of that would cause the actual computer to start unexpectedly flickering is it being on fire. You haven't really given us enough details. However, if you can't figure it out on your own, you should probably take it to a computer professional to have a look at it. There are lots of things that could cause the monitor to flicker, including "the monitor is going bad", and they have all kinds of different remedies.
More than likely the video card is going bad.
If you are using a vga connection, usually blue then you may have bent a pin on the connector, the cable may be bad, the monitor could be bad, your video card could be bad, or you could have the wrong driver or settings.
SMART long self test will find all the bad sectors of the computer and prevents the computer from being slow
You go to wiki.answers.com
If it isn't going into "sleep" mode (in which case just move your mouse), you may have a bad capacitor or diode in the monitor.
There really isn't any way to test the oxygen sensor to see if it is good or bad. If your check engine light is on you can take it to Autozone and they will hook it up to computer and if the oxygen sensor is bad, the computer will detect it.