Below, I listed directions concerning your issue with the black screen thing. As far as the freezing goes, I am not sure. (Before You Go On...)
You can change, modify and play-around with Display Settings from the Notification Panel.
This is where you can change the settings for why your lap top screen is blacking out. Follow these steps in order to change these options:
1)Connect your laptop to your Roku the way you normally do.
2)Once connected, use your TV (which I assume is what your using for the Roku?) to navigate;
3)Click on your notification setting & click 'All Settings"
4)You should be seeing the 'Display' panel
5)Scroll down to MULTIPLE DISPLAYS
6)Under the Multiple Displays section, and underneath multiple displays is a drop-down bar.
7)Here is where you change all of that. Click on 'Duplicate These Displays'
And BOOM, you should be able to see both screens on your TV & PC.
So hopefully this was able to solve your minor issue.
As far as the freezing goes, I am not sure. I would have that same problem in the past with my Tablet though. I never had issues connecting my PC to my Roku/TV but hopefully your able to solve the issue now that you can actually see what is going on!
“Surely I have contemplated the things of God.”
Joseph Smith Jr.