A graphics card not detected is almost always a connection or a power fault rather than a dead card. Before you buy a replacement, check four things: the monitor cable is plugged into the card and not the motherboard, the card is fully seated in the top PCIe slot, every power socket on the card is filled, and the power supply can still hold the load.

We build gaming PCs and we repair them, so this one comes across the bench regularly, and plenty of cards that arrive dead leave working. Here is the order we check them in, and the point where a card really is finished.

Start With the Monitor Cable

This is the answer often enough that we check it first, and we would rather you found it at home. If your processor has graphics built in, a cable in the motherboard's HDMI or DisplayPort socket gives you a picture with no involvement from the card at all. Windows then reports the display running on the integrated chip, and the card looks absent.

Look at the back of the case. The motherboard ports sit together in a block near the top. The card's ports sit lower down on their own bracket. Move the cable there and restart.

If your picture was coming from the motherboard, nothing is wrong with the computer as a machine. You have a card that is not being used, which is a much shorter problem than a dead PC.

Is the Card Seated, or Does It Just Look Seated?

A card can sit in the slot, look level and still not make contact across the whole connector. Heavy cards sag over a year or two, and the end furthest from the bracket drops a fraction.

Power everything down and take the card out properly: undo the bracket screws, press the latch at the end of the PCIe slot, then lift. Blow the dust out of the slot. Put the card back with your thumbs over the top edge and press until the latch clicks on its own. Screw the bracket back down before you close the case, because those screws are what stop the sag returning.

If the board has a second full length slot, try the card there. A card that works lower down but not in the top slot is telling you the slot is the fault, not the card.

Power: The Cable, the Connector and the Supply

Most cards need power from the supply as well as from the slot, and a lazy connector is a classic no-detect. Check both ends of every PCIe power cable, the card end and the power supply end. Where a card has two or three sockets, fill all of them, and run a separate cable to each one rather than doubling a single cable back on itself.

Newer cards use the 16 pin connector instead. It carries up to 600 watts against 150 watts for the old 8 pin plug, so there is a lot riding on it being pushed home, and the melted connectors you have read about were traced mainly to plugs that were not fully seated under load. The revised 12V-2×6 version changes the sockets so the sense pins only make contact once the power pins are seated properly, which is the industry quietly admitting how easy the old one was to get wrong. Push until it clicks, then check it again after you tidy the cables, because tidying is when they get pulled loose.

The supply itself is the last piece. A tired unit can run a machine perfectly well with no card in it and then give up the moment the card asks for its share. If the PC starts without the card and dies with it, suspect the supply before you suspect the card.

How We Check a Card That Will Not Show Up

Step six is the one that is hard at home and quick on a bench. Known good parts turn a guess into an answer in a few minutes, which is why we would rather test your machine than sell you a card you may not need.

Why Is My GPU Fan Spinning but Not Detected?

A spinning fan means the slot is delivering power to the board. That is all it means. Fans can spin while the processor, the memory or the PCIe link are doing nothing, and many cards leave their fans still at idle by design, so a motionless fan is not a verdict either.

Three things that do tell you something:

• The card appears in the BIOS. The board can see it before any driver loads.
• A known good card works in the same slot. The slot and the supply are fine, so your card is the suspect.
• Your card works in another machine. Then the fault is in the first machine, not the card.

Graphics Card Not Detected in BIOS: What That Narrows It To

If the board's own firmware cannot see the card, no amount of driver work will help, so stop downloading things. Restart, go into the BIOS and look for the slot under the PCI or PCIe configuration pages.

Three settings worth checking while you are in there:

• Primary display. Set it to the PCIe slot rather than the integrated graphics.
• PCIe link speed. Forcing the slot down a generation sometimes brings a flaky card back, which is useful information rather than a fix.
• Firmware version. An older board with a very new card is worth updating from the board maker's own support page before you conclude anything.

If the card still does not appear after a reseat, a different slot and a different power cable, the hardware is the problem and the next step is a bench test, not a purchase.

What Windows Is Telling You When the Card Is There

Sometimes the BIOS sees the card and Windows will not use it. Open Device Manager, look under display adapters and check for a yellow mark. Error code 43 means the graphics driver has told Windows the device is not working properly, and Microsoft's own steps are to update the driver, roll it back if the trouble started after an update, or uninstall it and let Windows reinstall it.

A clean driver reinstall settles a fair share of these. One that fails again within days is usually not a software problem at all, and we go back to the hardware list above.

When Is a Graphics Card Worth Repairing?

Less often than a laptop board is, and we will tell you that rather than take the job. A card is a dense board with a soldered processor and soldered memory, so component level work on one is real but specialist, and on a mid range card the labour can be worth more than the card.

Not worth the labour

• A browned or melted power connector on the card. The damage is rarely limited to the plastic.
• Chipped or lifted PCIe contacts, or a bent board from a cooler that was mounted badly.
• Speckles, lines and crashes from failed memory on a card several generations old.
• A reflow sold as a permanent fix. Heating a chip until the old solder melts can buy a few weeks. Our guide to motherboard and board level repair explains the difference between a reflow, a reball and a replacement.

Worth a look

A failed fan or cooler that has been cooking the card into shutdowns is usually a straightforward job, and so is a power connector that can still be replaced cleanly. Any card still inside the maker's warranty is worth checking with the maker before anyone opens it.