macOS Monterrey not installing

How long have you let it go?

Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold one of the following combinations on your keyboard. Command-R is generally recommended, especially if you never installed macOS Sierra 10.12.4 or later… How to reinstall macOS - Apple Support

Command (⌘)-R

Install the latest macOS that was installed on your Mac.

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

Shift-Option-⌘-R

Install the macOS that came with your Mac, or the closest version still available.

Guillex17 wrote:

When I download the update, it will ask me to restart the computer. Once it restarts it never shows the log in screen. I have to turn the computer off and turn it back on to see the log-in screen again. Once I log in the update icon is still in the dock, meaning the update seems to not be installed.

How can I fix this?

" When I download the update, " this wording implies Monterey was already installed and running. An update would be Monterey version 12.1 to Monterey version 12.2.1 latest version.

Can you clarify is this was the case or was this an UpGRADE from a previous version of macOS. If so, what version was installed before attempting the Monterey installation.

Point # 3 - Empty Space Requirements  >> If upgrading from macOS Sierra or later, your Mac needs 26GB of available storage to upgrade. If upgrading from an earlier release, your Mac needs up to 44GB of available storage. 

Point # 4 - Empty Space afterwards - it is suggested to keep at least 15% to 20% of the Drive Total Capacity as Empty Space for good operations of the computer and for additional updates to Monterey to download, expand and install.