I started to install mackeeper and my computer is frozen. I want to stop the installation

Be sure you don't install MacKeeper

Press and hold down the Power button until the computer shuts down. Wait 30 seconds then restart the computer into Safe Mode. This will hopefully prevent the MacKeeper installer from restarting. See How to manually remove MacKeeper from your Mac. When you finish removing it you do the following:

Repair the Drive for El Capitan or Later

1. Restart the computer and after the chime hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and press the Continue button.
3. Then select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid tab in the toolbar and wait for the Done button to activate. Click on it, then quit Disk Utility.
5. Select Restart from the Apple menu.

No you cannot, please post an EtreCheck report of your system. Navigate to EtreCheck.com and download the app. Then run it, it will produc a report of your system, copy and paste the entire report as your reply to this message.

Sure. See this article for help: How to Uninstall MacKeeper – Updated. You do not need to use EtreCheck for this easy task.