You also need to limit the current even if you use the right voltage.
This is a pretty good explanation:
http://www.instructables.com/answers/why-does-an-led-have-to-be-given-a-resistor-before/
And you probably didn't do your computer a favor by shorting the usb port...
I have a U2414H and will add a second one soon.
If you don't mind a bit of backlight bleeding in the corners, I can really recommend it!
BTW You don't have to use the stand, it's vesa compatible.