I have the same problem. Whenever i copy and paste my bitcoin address, it changes to another. But i noticed it only changes the bitcoin address, not any other address. so i was telling is there any way to fix this problem without removing/wiping my whole pc or os. i mean its too much work. Please help.
We can't do much to directly help you but I try to tell you what can you do.
At this point it is certain, your machine is infected with virus/malware. They only way is to find what that virus is and remove it. If you fail to do that you need to purge your system.
To remove malware I suggest you can use Malwarebytes Anti-Malware or Kaspersky Anivirus - these two helped me before with extremely pesky trojans which other antiviruses refused to clean or even find.
Are you a Hearthstone player? Because I heard about this type of malware hidden in third-party tool for Hearthstone.