The Advanced SystemCare (ASC), blocks the latest Steam update, so, the users cannot login to their account. In order to fix this, you need to uninstall the ASC, and then login to your account by running Steam Client. After that, you can reinstall the ASC or not, it's your choice. It will not block you again to play Steam games If you still cannot login, try reinstalling Steam, disabling antiviruses etc. Last solution is to find the program which blocks the Steam.