The computer can't be turned on, the fan turns on but the screen goes black-5 steps to self-check, 71% of them can solve it themselves

I. Symptoms: First distinguish which kind of "can't start the machine" you are

Press the power-on button, the case fan turns on, the indicator lights up, the keyboard and mouse may still have electricity, but the display has been black, prompting "no signal"-this article is talking about this kind. Another is that press the power-on button has no response, the fan does not turn on, the light does not light up, that is mostly the power supply or motherboard power supply problem, the processing idea is completely different. First distinguish your own situation, then start.

Second, the cause analysis: the fan is turning, why is it still black

Fan turn indicates that the motherboard has been powered on, but the machine did not pass the POST. According to the probability of our store encounter, there are several common reasons:

1. memory poor contact. Gold contacts oxidation or loosening is the first major reason for "fan to black screen." The machine has been idle for more than half a year, or in Guangzhou in March and April back to the south, this kind of fault obviously becomes more.
2. Graphics issues. The gold contacts is oxidized, the power supply line is not plugged in tightly, or the graphics card itself is damaged. CPU with nuclear display can be unplugged and tested with nuclear display first.
3. BIOS settings deranged. Motherboard button battery (CR2032) no electricity, or overclock parameters are not adjusted well, the machine will not light up.
4. Insufficient power output. After the power supply aging 12V power supply cannot support the CPU and graphics card, the fan can turn, but the belt does not move the whole machine to start.
5. Motherboard or CPU failure. The smallest but most troublesome, usually accompanied by repeated power-down restarts, diagnostic card running code abnormalities.

The first three categories account for more than 70%, and you can check them yourself first.

III. Self-help steps: 5 steps in sequence, don't jump

Turn off the power before starting, unplug the power cord, press and hold the power button for 10 seconds to discharge the remaining electricity; touch the metal shell of the chassis to release static electricity.

Step 1: Exclude the monitor and wires first. Is the monitor powered on? Is the input source selected correctly (many monitors do not automatically switch HDMI and DP)? For machines with separate displays, the cable should be plugged into the interface of the separate display. The motherboard interface usually has no signal. Try changing a monitor or TV. Don't disassemble the chassis as soon as you come up.

Step 2: Reseat the memory and wipe the gold contacts. Open the side panel, unplug the memory, rub the gold contacts back and forth with an eraser until it shines, blow off the rubber crumbs and then insert it back. The two buttons should be "clicked" tightly. Insert only one of the two memories for testing, and then change the other one. Change the slot to try in turn. This step can solve more than half of the black screen.

Step 3: Check the graphics card. If there is a core display, unplug the independent display first and connect it directly to the motherboard to light up. You must use the independent display, plug it again, rub your golden finger, and confirm that the 6pin or 8pin power supply cable of the graphics card is plugged tightly.

Step 4: Discharge BIOS. Find CR2032 button battery on the motherboard, pull it down and wait 5 minutes before installing it back on the boot. BIOS will restore the factory settings. Overclocking failure, black screen caused by setting disorder, this step can often be saved. Battery used for more than five years, conveniently replace a new one, a few dollars.

Step 5: Minimum system approach. Only keep CPU, a memory, power supply and nuclear display output, unplug hard drive, all USB devices and chassis front panel cable. Can light up, and then one by one back, installed to which black, which is the problem.

4. When must I hire a professional

After 5 steps, there is still a black screen, or any of the following situations, don't dismantle it yourself:

• Press the power-on button to instantly power down, repeated restart, mostly short circuit;
• Smell burnt smell, or see bulging capacitor on the motherboard, burn marks;
• The machine is still in the warranty period, self-disassembly may lose the warranty;
• There are no replaceable parts on hand, it's all about guessing.

At this time, continuing to toss will only increase the failure point. The desktop will be sent directly for repair or about on-site, doDesktop repairThe master has spare memory, power supply and diagnostic card in his hand. The replacement method can locate the specific parts in ten minutes, which is cheaper than buying accessories yourself. The laptop structure is precise, and the black screen self-examination is more conservative. See details.laptop repair.

V. Fee Reference

The above is Guangzhou Panyu market in 2026, the specific test results shall prevail.

6. Real cases

In March 2025, a customer in Panyu Shiqiao brought a PC build: i5- 9400F with MSI B360M MORTAR motherboard and Kingston DDR4 8GB memory. After half a year of idle, the fan turned on and the black screen had no signal. The customer bought a new power supply for RMB 230, but it was useless. After testing, we judged that the memory gold contacts was oxidized and caused poor contact. Remove the memory and clean the gold contacts with an eraser. After reinserting it, it will light up once. The charge is RMB 80 (including detection and burn-in test of the whole machine). The new power supply can actually be returned.

Every year, customers say,"I thought it was a big problem, so I bought accessories first." Remember: check the contact first, then replace it.

7. Local Service Portal

We are located at No.3-8 Jinlong Road, Dalong Street, Panyu District, Guangzhou, Panyu District, Nansha District. Tel: 18825126836 / 020-39029800, Mon–Sat 09:00-18:00.