Computer Turns On But No Display? How to Tell if It’s the Monitor, the Cable, or the PC

The tower powers up — fans spinning, lights on, maybe the familiar startup hum — and the monitor just sits there. Black screen, or worse, a smug little "No Signal" box floating around. A computer that turns on but shows nothing is one of the most common desktop problems we see in Somerville, and the good news is that the cause is usually one of a short list, and you can narrow it down at home in about five minutes.

The whole game is splitting the problem into thirds: is it the monitor, the cable, or the computer?

Step 1: Prove the monitor is innocent (or guilty)

1. Check the monitor's own power light. No light at all? The monitor isn't getting power — different outlet, different power cable if you have one. A monitor that won't turn on is its own repair, and it's cheaper to confirm now than after you've torn the PC apart.
2. Press the input/source button on the monitor. This fixes more "no display" calls than anything else I can put in an article. Monitors with multiple ports (HDMI 1, HDMI 2, DisplayPort) love to sit on the wrong input. Cycle through all of them.
3. Test the monitor on anything else. A laptop, a game console, a streaming stick. Picture appears? Monitor's fine — move on. Still dark on a known-good source? You've found your problem without opening a case.

Step 2: The cable and connection

1. Reseat both ends. Unplug the video cable at the monitor and at the PC, look at the pins, plug it back firmly.
2. Swap the cable if you can. HDMI cables fail more often than people think, and a marginal cable can work for years then quit after being bumped.
3. Confirm you're in the right port on the PC. This is the big one for desktops with a graphics card: if your tower has ports up high near the fans (motherboard) and ports down low on a horizontal card (graphics card), the monitor belongs in the graphics card's ports. Plugging into the motherboard when a dedicated GPU is installed gets you a black screen on many systems.

Step 3: Now suspect the computer

If the monitor and cable pass, the PC is powering on without actually starting up — "on" and "booting" are different things. In order:

1. Force a full restart. Hold the power button 10 seconds, wait, power on. Listen for a single happy beep (some boards) and watch for keyboard lights.
2. Unplug every USB device except keyboard and mouse. A failed USB gadget can hang the boot before video appears.
3. Reseat the RAM. Power off and unplug the tower, press the case's power button once to drain, open the side panel, release the clips on each memory stick, and click them back in firmly. If there are two or more sticks, try booting with just one, then the other. Failed or unseated RAM is the single most common cause of fans-spin-no-video on the machines that cross our bench.
4. Reseat the graphics card the same way — release the slot latch, pull it, click it back, and make sure its extra power cables from the power supply are snapped in fully.
5. Listen and look for codes. Repeating beep patterns, or a small two-digit LED readout on the motherboard, or four little labeled lights (CPU / DRAM / VGA / BOOT) — each is the board telling you which component failed the handshake. Write down what you see.

Just built or upgraded this PC? Read this part

A brand-new build with no display is its own genre. The usual suspects: the 8-pin CPU power cable at the top-left of the motherboard not plugged in (the 24-pin alone isn't enough), RAM in the wrong slots (two sticks usually go in slots 2 and 4 — check the manual), the monitor plugged into motherboard video on a CPU with no integrated graphics, or a stick of RAM the board wants a BIOS update to accept — a mismatch we've written up in the RAM and motherboard mismatch that keeps custom PCs from booting. Our full checklist lives in how to fix a custom-built PC that won't turn on, and when you've had enough, our custom PC diagnostic service exists for exactly this machine.

No display FAQs

The monitor says "No Signal" — what does that actually mean?

The monitor is working and listening, but nothing is talking to it. That vote goes against the cable, the selected input, or the PC's video output — and clears the monitor's panel itself. Cycle inputs first, then cable, then the PC steps above.

My screen is black but I can see a mouse cursor.

Different problem entirely — Windows is running and video works; the desktop shell crashed. Press Ctrl+Alt+Del, open Task Manager, File > Run new task, type explorer.exe, Enter. If that's a weekly ritual, something deeper is wrong and worth a look.

It shows the manufacturer logo, then goes black.

Video hardware is fine — Windows is failing to start. That's a software/drive problem, cousin to the errors in our boot device not found guide.

It worked yesterday and nothing changed. Really?

Something changed — it just wasn't you. Windows updates swap display drivers overnight, power flickers scramble monitor handshakes, and cables creep out of ports a millimeter a month. That's why the five-minute split test earns its keep.

Laptop instead of a desktop?

Same logic, different steps — flashlight test, external monitor — covered in our guide to a laptop that turns on but the screen stays black.

When to bring it in

Bring the tower in if reseating RAM and the graphics card changed nothing, if you're getting beep codes or debug lights, if the "no display" comes and goes with warmth (starts fine cold, blanks out hot — a classic failing-GPU tell), or if you'd simply rather not open the case — no judgment, that's the job. A failing graphics card gets confirmed on our bench with known-good parts, and if it does need replacing, our graphics card replacement service handles sourcing sanely. Everything else lands under desktop PC repair in Somerville.

Diagnostic is $75, credited toward the repair. You get the actual cause — monitor, cable, RAM, GPU, board — and a straight quote before we fix anything. Most no-display desktops are diagnosed within a day or two of drop-off.

Directions to our shop

Dave's Computers is at 75 North Bridge Street, Somerville, NJ 08876, in downtown Somerville just off Main Street.

From I-287, take the exit for US-202/206 toward Somerville, follow signs into downtown, and turn onto North Bridge Street from Main Street. From the Route 22 corridor in Bridgewater or Bound Brook, head south on Route 202/206 or Adamsville Road into downtown. We're a few minutes from the Somerville Circle. Street parking is available on North Bridge Street, with municipal lots within a short walk.

We're a drop-off shop — no appointment needed. Hours: Monday–Friday 10am–5pm, Saturday 9am–2pm. Bring just the tower — we have monitors, cables, and power cords on the bench. If the problem might be your monitor, bring that instead (or too).

$25 off for new customers

First time in? Mention this article at drop-off and we'll take $25 off your first repair. The $75 diagnostic is still credited toward the work. One per customer, new customers only.

Or call 908-428-9558 and tell us what the lights and beeps are doing — we can usually point you at monitor, cable, or PC in one phone call.