# Fix a black screen or missing video

## Symptoms

- The viewer opens, the session shows as connected, but the picture stays black.
- The picture freezes while the customer is doing something, often when Windows asks for permission.
- The video is dimmed and a notice says **Reconnecting…** or **Customer reconnecting…**.
- On a Mac, a card says **The customer has not allowed screen sharing yet**.

## Likely causes

- The connection to the server or to the customer's computer dropped, and the viewer is waiting for it to come back.
- On a Mac, the customer has not allowed Screen Recording.
- On Windows, the customer is looking at a UAC prompt or the lock screen, which a session that is not running as administrator cannot capture.
- The network lets the session start but blocks the video itself.
- The computer's graphics driver has trouble with hardware video encoding.

## Check the viewer first

1. Look for a notice over the video. **Lost connection to the server. Trying again in N s.** means your own connection dropped; **Lost connection to the customer's computer. Waiting up to 2 minutes for it to come back.** means theirs did. The picture returns by itself when the connection is back.
2. Look at the status strip along the bottom of the viewer. If the frame rate stays at `0 fps` while the session is connected, no video is arriving. Go on with the checks below.
3. If the customer has more than one monitor, switch to another monitor in the viewer to see whether only one screen is affected.
4. Reload the viewer page. If it says **This page is out of date**, click **Reload**.

## A Mac shows nothing

macOS blocks screen capture until the customer allows Blink under **Screen & System Audio Recording**. The viewer shows the steps to read out to the customer, and **Ask the customer again** opens Blink's permission window on their Mac. See [Fix missing Mac permissions](/troubleshooting/mac-permissions/).

## Windows freezes on a UAC prompt or the lock screen

Windows shows UAC prompts and the lock screen on a separate, protected desktop. A Blink session running as the signed-in user cannot capture it or click on it, so your picture stops changing until the prompt is gone.

1. Ask the customer to answer the prompt themselves.
2. To work through prompts yourself, click **Run as admin** in the viewer, enter an administrator's user name and password and click **Elevate** (or click **Use UAC prompt** to have the customer approve it with their own administrator account). The customer approves one Windows prompt. From then on, Windows shows UAC prompts on the normal desktop for the rest of the session, so you can see and answer them. Blink puts the Windows setting back when the session ends.

In Access sessions Blink already runs with full rights, so it can show the lock screen and sign-in screen. Use the **Ctrl+Alt+Del** button in the viewer to reach the sign-in screen.

## The network blocks the video

A session can connect (the customer's tool shows it is connected, you can see the session in **Sessions**) while the video itself cannot get through. Blink then keeps trying to reconnect.

1. Try from another network on your side, for example a phone hotspot. If the picture appears, your network is blocking the video.
2. Check the network on the customer's side as described in [Fix a Blink agent that will not connect](/troubleshooting/agent-wont-connect/).
3. If you run your own Blink server, make sure the session and relay ports listed on that page are open, and that **Hand out TURN servers to agents and viewers** is on in **Instance** › **Security** › **TURN relay**.

## Graphics driver problems (Windows)

Blink uses the computer's hardware video encoder when there is one. If the hardware encoder fails, stalls or refuses to start, Blink switches that screen to software encoding on its own and tries the hardware encoder again later. You normally see at most a short pause.

You can see which encoder a session uses: in **Sessions**, open the session and look at **Encoder** under **Remote computer**. `openh264` means software encoding; `mf` (Windows) or `vt` (Mac) means the hardware encoder.

If the video still stays black or garbled on one Windows computer, start a session with hardware encoding switched off:

1. End the current session and create a new Support code. The customer downloads the tool again.
2. The customer opens Command Prompt in their Downloads folder and starts the new download with:

   ```bat
   blink-xxxxxxxxxxxx.exe --encoder openh264
   ```

   using the exact file name.
3. If the picture now works, the computer's graphics driver is the likely cause. Updating the graphics driver usually fixes it for later sessions.

## When to contact IZT

Contact [IZT](https://izt.app) if the picture stays black on a connected session after these checks. Send the session id, the remote computer's Windows or macOS version, and the session log. See [Collect logs for IZT support](/troubleshooting/collect-logs/).