You can force close the application through the Task Manager. Press CTRL + Shift + Escape, then switch to Processes tab and locate the executable of the file. With the file selected, press End Task and it should close. If it doesn't reboot the PC and start it in Safe Mode by pressing F8 continuously until the service menu appears.
After this, you can use Revo Uninstaller. Even if it can't uninstall the application normally, it will force it to uninstall by wiping out all traces of its presence from the system.