find the demos system requirements, then look at your current features. Can your pc take it? or maybe u have a dreded grafics card that wont work for it check in the read me for the list of hell
i was playing online and Corolios... i forget how to spell his name... and another dude from 2015... started with an S really helped me out... they were GREAT... giving on the spot support for the demo... ive never seen that kind of help from a game before..
either way...
all i had to do was update my geforce 2 drivers... which were one step out of date... because i was getting strange all black screens too
give it a try mate