When the computer is turned on, the processor accesses the ROM chip, which contains the BIOS codes - the boot program. The BIOS initiates the launch of a POST - a computer hardware autotest. After successful completion of the test, control is transferred to the operating system. If the BIOS does not start, this indicates a problem with the components of the system unit.
Power supply problems
Over time, even a good power supply loses its performance, and its characteristics cease to correspond to the declared ones. For example, capacitors on its board may swell or explode. Visually, it looks like a convex end surface or a small amount of gel around the capacitor electrodes. Such damage is easy to detect and the damaged element can be replaced. However, even in good-looking capacitors, the electrolyte dries up, and the power supply unit does not work correctly. For example, there is no "cold start" of the system unit; several reboots are required for the power supply elements to warm up and the computer to turn on. If the BIOS does not start when you turn on the power, try replacing the power supply with a known good one.
ROM issues
The ROM chip is powered by a round battery located next to it on the motherboard. The nominal voltage of this battery should be 3 V. If it drops to 2.7 V, problems may begin. Replace the battery with a new one, remembering how it should be installed.
Changes in BIOS settings can also cause problems. In this case, resetting the settings to the default ones will help. Unplug your computer from the wall outlet by pulling out the power plug and carefully remove the battery. Use a screwdriver to bridge the electrodes in the slot where the battery was installed and hold for 30 seconds.
Problems with other components
Unplug the computer from the network and disconnect hard drives, CD and DVD drives from the motherboard, remove RAM modules and all expansion cards from the slots. Only the power supply and processor should remain. Turn on your computer. If the speaker beeps, then the BIOS is starting up, and everything is in order with the motherboard and processor. Start alternately connecting RAM, video card, hard drive, drives, etc. to the motherboard. Previously, it would be very useful to wipe the contact pads of the video card and RAM modules with an ordinary school eraser. Of course, you must unplug your computer from the electrical outlet before each connection. If after connecting any element the BIOS does not start, you have found the culprit of the problems.
Problems with the motherboard and processor
If the system unit does not start with the motherboard + processor + power supply, carefully examine the motherboard for swollen capacitors - this is the most common malfunction.
The power button on the front panel of the system unit may not work. Find the connectors on the motherboard to which it connects (usually labeled Power or PWR). Disconnect the button from the motherboard and bridge the connectors with a screwdriver. If the system unit starts up, you will have to change the button.
Remove the heatsink and cooler from the processor, place your finger on it, and turn on the computer. You can keep the processor energized without a heat sink for no more than 4 seconds. If the processor starts to warm up, then it is working properly. Turn off the power immediately by unplugging the power cord.
Lubricate the sole of the radiator with fresh thermal paste, after wiping off with a dried cotton swab dipped in alcohol. Install the heatsink and cooler on the processor, turn on the computer, and check if the fan spins.
Check the south and north bridges for heating (2 large microcircuits, possibly with installed heatsinks, on the motherboard). If overheating occurs, it is best to contact the service department.
