Your computer may have crashed. Restart by pressing Ctrl + Alt + Del on the keyboard. You will see ‘Task Manager’. Select the option within here to force a restart.
If this doesn’t work, press and hold the power button on the front of the PC unit until it restarts.
Note By doing this you will lose any unsaved changes you might have made to your system so be sure to save regularly if editing/creating themes or making changes.
If the problem persists, please submit a support request by clicking the 'Submit Request' link at the top of this page.