hi why every time mackeeper pop i can't use safari

First try

Stop pop-up ads and adware in Safari

Remove unwanted adware that displays pop-up ads and graphics on your Mac

Next:

Malwarebytes for Mac (was Adwaremedic)

I am anticipating that the great Linc Davis will recommend you follow the instructions below (he may even provide you more)

Stop pop-up ads and adware in Safari - Apple Support

Whatever you do, do not install any anti-virus, any adware, or malware cleaning apps. They do more harm than good.

All you need to remove malicious software is the Finder and a web browser (that's one of Linc's quotes!!)

Force quit Safari from the  menu and reopen with the shift key held down. If that doesn’t work, disconnect from the Internet, open Safari, and then reconnect to the Internet. See link for other suggestions.

Safari -Tech support scam pop-ups

You'll find that Apple's instructions there are woefully outdated and incomplete. There are entire groups of adware not even mentioned there, and many of the ones that are have changed so much that they cannot be removed completely using Apple's instructions.