The application is running by default in background even if you close it using the X icon. In order to stop it, you need to right-click its icon from System tray and to press Quit:
Alternatively, press Alt + Ctrl + Delete key combination, open Task Manager, press the Processes tab and close all PowerSuite instances using the End Process button:
After that, go to Start, type msconfig and open the utility. Click the Startup tab, un-check the box next to PowerSuite, click Apply and then OK.
If you still have issues, remove the software from your computer using its uninstaller or Add or Remove Programs feature (Control Panel > Uninstall a program), perform a full system scan using your antivirus program or a utility from Software Informer database and download and install the PowerSuite application again.