@MDK1 We'll need a little bit more information in order to assist you:
Which version of Windows are you running? If Windows 10, do you know the Windows 10 version number?
What is your present CCleaner version number? Is it a free, paid or trial copy?
When did it stop working for you? Was there anything that you installed or changed on your system prior to CCleaner stopping working?
Will your existing installation of CCleaner run if you go to C:\Program Files\CCleaner, right-click on CCleaner64.exe and select "Run as Administrator"?
What happens when it stops working? Does it appear and disappear after you run it or does it fail to load entirely? Are any error messages displayed?
Which AV are you using, and when did you last update it?
Are you using a firewall or a custom etc/hosts file and, if so, have you added any rules to block CCleaner?