1. First work out which kind of "won't start" you have
You press the power button, the case fans spin, the power light comes on, the keyboard and mouse may even light up, and the monitor stays black with a "no signal" message. That is the case this article is about. The other case is a power button that does nothing at all: no fans, no lights. That is almost always a power supply or mainboard power problem, and the approach is completely different. Work out which one you have before you touch anything.
2. Why the fans spin while the screen stays black
Fans turning means the mainboard has power, but the machine is not clearing POST. Here they are, sorted by how often we see them:
- Memory not making contact. Oxidized or loose gold contacts are the single biggest cause of "fans spinning, screen black." Machines that sat idle for more than six months account for a noticeable share of them, and so does the humid spring spell in Guangzhou in March and April.
- Graphics card problems. Oxidized contacts, a power cable not fully seated, or a dead card. If the CPU has integrated graphics, pull the card and test on the mainboard output first.
- BIOS settings out of order. A dead CR2032 coin cell on the mainboard, or an overclock that was never stable, will keep the machine dark.
- Not enough power output. An aged power supply cannot hold 12V under the load of the CPU and card. The fans still turn, but the machine will not come up.
- Mainboard or CPU failure. The smallest share and the most trouble, usually with repeated power loss and restarts, or a POST card showing nonsense codes.
The first three account for more than 70% of cases, and you can check all of them yourself.
3. Five steps, in order, without skipping
Before you start: shut down, unplug the power cord, hold the power button for ten seconds to drain the residual charge, and touch the bare metal of the case to discharge static.
Step 1: rule out the monitor and the cable. Is the monitor on? Is the input source right? Many monitors do not switch between HDMI and DP on their own. On a machine with a discrete graphics card, the cable has to go into the card's output, because the mainboard output usually stays dead. Try another monitor or a TV. Do not open the case as your first move.
Step 2: reseat the memory and clean the contacts. Open the side panel, unclip the module, rub the gold contacts with a pencil eraser until they shine, blow off the eraser debris and push it back in until both clips click. With two modules, test one at a time and try the slots in turn. This step alone fixes more than half of all black screens.
Step 3: check the graphics card. If the CPU has integrated graphics, pull the discrete card and connect the monitor to the mainboard. If you need the card, reseat it, clean its contacts the same way, and confirm the 6-pin or 8-pin power cable is fully seated.
Step 4: clear the BIOS. Find the CR2032 coin cell on the mainboard, lift it out, wait five minutes, put it back and boot. The BIOS returns to factory settings. A failed overclock or scrambled settings that leave the machine dark often come back at this point. If the cell is more than five years old, fit a new one while you are in there; they cost a few RMB.
Step 5: minimum system. Leave only the CPU, one memory module, the power supply and integrated video. Unplug the drives, every USB device and the front panel connector. If it boots, add the parts back one at a time. The part that turns the screen black again is the culprit.
4. When to stop and bring it in
If five steps leave you with a black screen, or any of these apply, stop taking it apart:
- The power button causes an instant shutdown or a restart loop, which usually means a short circuit.
- You can smell burning, or you can see a bulging capacitor or a scorch mark on the mainboard.
- The machine is still under warranty, and opening it yourself may void it.
- You have no spare parts to swap in, so everything is guesswork.
Continuing at that point only adds one more fault to chase. Bring a desktop in or book a visit; our desktop repair technicians carry spare memory, power supplies and a POST card, and substitution finds the faulty part in ten or fifteen minutes, which is cheaper than buying parts to guess with. A laptop is a more delicate assembly, so be more conservative with a black-screen laptop; see laptop repair.
5. Price reference
| Item | Price | Notes |
|---|---|---|
| Diagnosis and assessment | RMB 50-150 | In-store check, quoted before any repair |
| Memory contact clean and reseat | RMB 50-80 | Includes a full boot test |
| BIOS clear and settings recovery | RMB 50 | Can be done on site |
| Power supply replacement, including testing | RMB 80 labor plus the unit | A rated 400W unit from Segotep or Huntkey starts around RMB 180 |
| Mainboard power repair | RMB 200-400 | Quoted after the board is out and inspected |
Guangzhou Panyu prices for 2026; the test result decides the final quote.
6. A real case
In March 2025 a customer in Shiqiao, Panyu, brought in a build: an i5-9400F on an MSI B360M MORTAR with a single 8GB Kingston DDR4 module. It had been idle for six months, and when he powered it up the fans spun and the screen stayed black. He had already bought a new power supply for RMB 230, which changed nothing. We tested it and found the memory contacts oxidized and making poor contact. Out came the module, a few passes with an eraser, back in, and it posted first try. The charge was RMB 80, including the test and a burn-in run. The new power supply was still returnable.
Every year someone says "I assumed it was something serious, so I bought the parts first." Check the contacts before you replace anything.
7. Where to find us
We are at 3-8 Jinlong Road, Dalong Street, Panyu District, Guangzhou, and we cover Panyu and Nansha on site. Phone 18825126836 or 020-39029800, Monday to Saturday, 09:00-18:00.