If you have the installation disk of Windows operating system, then I recommend you boot from it. Insert it and then press the button corresponding to Boot Selection menu. Choose the DVD and boot. On the installation page, click on Repair then use Startup Recovery. Start the process and restart the computer when it finishes, then the computer will boot again.
In the future, use something safer instead of Reg Pro Cleaner. For example, CCleaner is a good application for this purpose.