Installed new screen and touchscreen not working

You could have a few issues. Lets start with where you got your replacement parts from. If you purchased them from ebay, amazon, wish, craigslist, or aliexpress, odds are you got a junk screen. But if you ordered it from a reputable parts supplier, you may not have a firm connection. Try this next step, even if you did buy a screen from those suppliers. Open it up and inspect the connectors and the components around them. Make sure the connectors aren’t damaged or missing any components around them. After that, you can reseat them and “Frankenstein” the device together. If possible, connect the battery and power on the device while it’s still apart and make sure the screen works. I do this all of the time in my shop before I install parts to make sure they work. If the screen works, then you should be good to put it back together. If not, you probably have a defective screen. You can reach out to the supplier you purchased from and send it back for warranty if possible.