As Stranger said, safe mode could be the solution here. In case it's not, though, here are a few more things you can try.
Turn off the console and take out any game cartridge, but leave the sd card in. Make sure the sleep switch is off, then turn the console back on and leave it alone for up to 15 minutes. If it boots by then, it's fixed and good to go
Check the volume slider to make sure the sound is on. If it's not, and you hear sound after turning it on, you probably have a broken display
If those two don't work, open the console up and reseat the connections, particularly the display cables and any that look loose or out of place