On minecraft, why won't a portal work in the nether world?

Did you build it correctly?

10 blocks in total (without the corners)
4X3 and lit with a flint and steel, I don't see why it wouldn't work unless you have mods or plugins stopping it from working.

Hmm? What do you mean the portal isn't working?

If you in a server ask others.
Singleplay:

Place 5 blocks in the left and right. Make sure the obsidian pillars are separated 2 blocks. Place 2 blocks in the space between the pillars. Upper space also fill. Lit with flint and steel. 14 blocks, obsidian. 10 blocks if economical version

Last time i checked, you can't build end portals (but that was like 1.5)

Unless you aren't building it right, you build it like this

[o] = obsidian

[o] [o]
[o]. [o]
[o]. [o]
[o]. [o]
[o] [o]