The operating system (OS) is the backbone of a computer, enabling it to function smoothly and efficiently while providing a platform for applications to run. 

Popular operating systems are Windows, macOS and Linux.

If your operating system has stopped functioning correctly, or has been compromised, not only will your computer slow down, it may also be unsecure.

Your options are:

Upgrading your OS:

Most OS providers offer free upgrades to the latest version. Depending on hardware limitations, it might not always be the best option or even available to upgrade.

Benefits to upgarding are:

1. New Features and Improvements: Upgrades often bring new functionalities, improved user interfaces, and enhanced performance.
2. Security Enhancements: Newer versions include patches for vulnerabilities and better protection against malware and cyber threats.
3. Compatibility: Upgrading ensures compatibility with the latest software and hardware, which might not be supported by older OS versions.
4. Support: Manufacturers eventually stop supporting older OS versions, meaning no more updates or technical support.

Repairing an OS:

A repair could fix a lot of problems on an OS such as:

1. System Errors: Over time, an OS can develop errors or corrupt files that need fixing to restore normal functionality.
2. Performance Issues: If the system is running slow or experiencing frequent crashes, repairing the OS can help resolve these issues.
3. Malware and Viruses: Repairing the OS can be necessary to remove malware or viruses that have compromised the system.
4. Failed Updates: Sometimes, updates can fail or cause issues, requiring repair to ensure the system runs smoothly.

Reinstalling an OS:

If you are already on the latest OS version but are still experiencing issues, a complete reinstall can generally fix all problems (unless hardware related). 

This can also be performed to reset the computer if you want to sell or remove all data.

1. Start Again: To reset the computer to a version of the OS without any other settings or files.
2. New Device: When setting up a new computer, an OS needs to be installed to make it operational.
3. Custom Builds: For custom-built PCs, users need to install an OS to start using the hardware.
4. Switching Platforms: Users might want to switch from one OS to another (e.g., from Windows to Linux) for various reasons like preference, specific software requirements, or performance.