ASUS PRIME B450M-A II: SATA 5/6 missing after M.2

Match the symptom to the upgrade

This rule is especially relevant when an existing SATA SSD, hard drive or optical drive disappears immediately after an M.2 installation. Six physical connectors do not guarantee six simultaneously usable connections.

Check the II suffix. Similar PRIME B450M names are not a substitute for this model's documentation.

Locate and move the affected cable

1. Shut down, switch off the power supply and disconnect mains.
2. Note the current cable positions or take a reference photo for your own use.
3. Find the SATA6G labels using the motherboard layout. Do not infer numbers from cable colour or proximity to the edge.
4. If the missing drive uses SATA6G_5 or SATA6G_6, move its data cable to a free SATA6G_1–4 connector. Retain the drive's power connection.

Verify detection before repairing Windows

After reconnecting power, check firmware storage detection. If an existing system drive is detected but Windows does not start, inspect the boot selection before attempting installation or repair. A cable move does not require erasing a working disk.

If firmware detects the drive but Windows does not show a volume, preserve that distinction in your notes. A filesystem or partition problem is different from a disabled physical port.

If all available ports are occupied

Plan which devices must remain attached. Removing the M.2 drive can restore the shared pair, but may also remove your operating system. Check the entire arrangement before choosing that tradeoff.

A storage-driver installer cannot remove the documented sharing rule. If the drive still fails on a free supported port, check its power, data cable and detection in a known-working configuration.

Do not initialize a disk with existing data just to make it appear in a file browser. Establish the hardware path first, and record the working arrangement for the next upgrade.