Yes Meg is right you use the ESC key to leave the Presentation at any time.
I tried the Lighthouse one, downloaded it and it worked OK. If you are overloading your CPU hit CNTL ALT DELETE and see if SYSTEM is running about 50% with nothing else running it should be about 2%.
If it is high, instead of just powering down and rebooting. Power down and cut the electrical supply entirely with the switch at the top back of your computer. Then switch back on again and reboot.
thanks.. did check .. % usage varies (keeps changing) between 4% & 60 %
curious
Next time I turn off I will try what you suggested. I never knew there was a power button on back..