Did it beep or give any indication that it turned on or got power at all?
Edit:: So it gets sound. That's really good! At least it's still getting power. It's probably a connection issue.
Admittedly I've never taken apart a Tama, but I've lots of experience in general electronics.
My guess is there is a connection loose, not in, or damaged. I'd take it back apart carefully and make sure everything is connected well.
Edit Again::::
Check out this thread
https://www.tamatalk.com/IB/topic/156214-debugging-a-tamagotchi-v6music-star/
It is actually about finding the v6 debug, but the beginning and second post have some great info about taking apart and putting the Tama back together.
From the guides I watched, and the reading I've done... It seems that the LCD screen's pixels are lit up by the gold contacts on either side of the "main chip" connecting with the soft pink things on either side of the LCD panel. Make sure the soft pink things are securely attached and making good contact with the gold contacts.
Also, be sure you still have the foam piece that went behind the LCD and cardboard background. Please see Binary's post for a picture:
https://www.tamatalk.com/IB/topic/156214-debugging-a-tamagotchi-v6music-star/?do=findComment&comment=2549286
Lastly, this post
https://www.tamatalk.com/IB/topic/156214-debugging-a-tamagotchi-v6music-star/?do=findComment&comment=2549286 has some great inside shots of the LCD placement. It is a V4, but it might help you to spot the issue with yours!
I really don't think you've busted it yet. Unless you've done actual damage to the LCD or the board, I think you can fix it. But I also think if you'd of done real damage, you wouldn't be getting sound.
Good luck!