Mac Reviver Info
If software "Mac Reviver" tools don't work, the problem might be physical. Heat is the enemy of performance. When a Mac gets hot, the CPU throttles (slows down intentionally to prevent damage).
Before spending money on a commercial tool, you should attempt a manual revival. If you are technically inclined, this "manual reviver" method is free and often effective. mac reviver
Here is a secret most users don't know: When you drag an app to the trash, you often leave behind "kext" files and support libraries. A quality reviver performs a thorough uninstall, nuking every last trace of that app you deleted six months ago. If software "Mac Reviver" tools don't work, the