Click on the power button and hold down for 5-8 seconds. This will shut the system down in what’s known as a ‘cold boot’. Its not something you should do often, but in cases you can’t do anything else, its useful to know.
Once you restart, the computer might ask to run a scan or start in safe mode. You should run some maintenance programs, just to be sure to correct any issues.
On a side tip, you should change settings of programs so that nothing but Windows and your anti-virus starts up. You can go to Start>All Programs, then select the Startup folder. Delete icons in that folder. It won’t delete the program, but will shut down the programs that are starting up with your system.