Welcome to the HP Forums.
I see that your touch screen on your Envy TouchSmart has stopped working. I will do my best to help you with this.
I would just like to clarify exactly what the issues is. Is it just that the "touch" portion of the screen isnt' working? Or is the display not working at all (blank/black ect.)? Knowing this will allow me to accurately assist you with the issue.
As it is, from reading over the post I will provide you with some suggestions.
If it's a "touch" issues.
Start by making sure all the drivers that can be updated are up to date. You can do this by going to this link: HP ENVY TouchSmart 14-k100eo Ultrabook Drivers. Click on the "Scan Now" button, it will check your computer for anything that needs to be updated and provide you the driver updates. Just follow the utility.
If that alone doesn't correct the issue, then I would like you to read over this Microsoft post on the issues: Touch Screen not working after upgrade to Windows 8.1.. It explains how to Calibrate Touch. This may help you as well.
If it's that the screen is blank/black:
Try running through this document: Troubleshooting Black Screen Displays with No Error Messages During Startup or Boot.
Please let me know how it all goes, I hope it's able to help you out. Thank you for posting on the HP Forums.