That is usually associated with an error on the web page you are viewing.  It's not an error in the PC. You shouldn't have to reboot the PC, just hold the CTRL and ALT keys down and press the DELETE key if it's hung up and then access the Task Manager and "End" the Application (in this case your browser (e.g. Internet Explorer).   
All of a sudden, I'll get this popup: Message From Webpage, Stack overflow at line 25.  Everything on the screen freezes, I've had to restart the pc before.:emotion-9:
webpage freezes