Clear the CMOS

Clearing the CMOS resets the BIOS to its factory default state.  Depending on the motherboard type, there will either be a jumper or a 2 solded point of which needs to be shorted out.  A jumper system will usually be at 1-2 for normal of which must be shorted to 2-3 for resetting the BIOS

WARNING:
the system MUST be turned OFF when setting the jumper 2-3 (for a few seconds) and MUST be returned to 1-2 before turning the system back on, failure to do so will damage the board!

System Loses Time and Settings  

The motherboard's battery is dead, replace it (reading should be 3.0v at the least 2.8v)

Troubleshooting a dead board (no Beep)

If the system turns on but there is no boot-up, blank screen and no  BIOS Error Codes
Remove all add-on cards
Disconnect all hard drives and components
Connect only the keyboard and Monitor

If when turning the system on the keyboard LED's do not blink at all or if when turning the system on the keyboard LED's continuously blink the BIOS or main controller is damaged

Electrolyte Capacitors

Some time ago a mistake in the stolen formulation of the electrolyte used in a capacitors resulted in the manufacture of many motherboards with defective electrolytics.

Electrolytic capacitors do have a specified lifetime and even quality electrolytic capacitors will fail in time. That is one reason that more tantulum capcitors were used on quality motherboards in the "old days."
So far, the only motherboard maker to admit to the problem is ABIT and the only major PC maker to acknowledge being affected is IBM

System runs slow, sluggish

As the CPU Chip operates, it generates heat which in turn, attracts dirt and dust on the Heat Sink. Remove all dirt and dust by using compressed air or a soft tip brush.

Guide to installing a heatsink

Clean the surface of your CPU with a soft cloth, do not use any chemicals or cleaning agents.

Apply ONE DROP of paste, once the heatsink is securely fitted the paste will spread evenly and thin onto the entire surface of the CPU. Applying too much paste will smother the surface and not allow any heat to reach the heatsink.

Securely fit the heatsink taking note that the four fasteners are EVEN
If the heatsink is not evenly fitted onto the CPU it will not allow for any cooling.

Use your BIOS or any software to read the temperature rise when in heavy load (playing games or using software) and visa versa when the system is idle.  If the difference is substantial (more than 10 deg) then your heatsink is incorrectly installed and needs to be re-installed.

Heatsink Paste

Once the CPU heats up the paste will harden up and form the shape of the warped portions of the heatsink.  There is no manufacturing process that allows for a dead-even surface of the heatsink to be produced, which is why we use paste to fill in the gaps of a warped heatsink (these gaps are microscopic)

Once your remove the heatsink from the CPU you will cause cracks to form in the hardened paste.

Do not re-install the heatsink with the same paste

Troubleshooting a dead board (with Beep)

If the system turns on but there is no boot-up, blank screen beeps

Check your power supply and that the fan is working properly.
Check that the mobo is firmly in place and grounded properly.
Look for any loose cards (graphics, sound, etc.) Examine if there are any broken bits or any suspect rattling noises.
Check connections for keyboard, mouse or other peripherals.
Replace the RAM sticks which may be faulty.
Re-install all the original drivers and software which came with the board initially.
You can try to clear the CMOS memory. 

Checking your power supply voltages

To get an accurate voltage reading on those motherboards requires opening up the computer and checking the voltages with a voltmeter. There are three main voltage values to check: 3.3 volts, 5 volts, and 12 volts. According to the official specification all three of those voltages must be within 5 percent. But in real life it's better if they are closer than that. So 3.3 volts should be between 3.2 to 3.4 volts. 5 volts should be from about 4.8 to 5.2 and 12 volts should be from 11.6 to 12.4. If the voltages are outside of that range, it's not proof of a power supply problem but it's not good. Some video cards tolerate voltages which are off better than others. With most new video cards, the 12 volt value is the one which is most likely to cause problems.