Since you can't shut off your computer normally, press and hold the power button up until the CPU shuts down. Press the Power button once again to turn on your computer and as soon as the CPU lights up, press the F8 button on your keyboard and keep doing so until the "Advance Boot Option" appears on your screen. Use the arrow keys on your keyboard to scroll down and select "Safe Mode with Networking" from the list of boot options. Press the Enter key on the keyboard and your computer will restart. What Safe mode does is that it allows your computer to run using only the most basic and necessary program without using third-party applications, including the viruses. This way, any malware that may exist in your PC will stay inactive and can be easily removed.

Summary:
Turn off your computer. Access the Advance Boot Options. Boot into Safe mode.