There is a certain formation that the primsarine, dark prismarine, prismarine bricks or sea lanterns need to be in to activate the conduit.
Empty spaces can be anything.
When activated, conduits give the "Conduit Power" effect to all players in contact with water or rain, within a spherical range of 32-96 blocks. This effect stops the breath meter from decreasing, gives underwater night vision and increases mining speed. Conduits can be activated in any biome and at any height or depth.
To activate, a conduit needs to be surrounded on all sides by water (source blocks, flowing water, and/or waterlogged blocks) and the conduit and water must be enclosed in an activation frame. The frame is built up of blocks in three 5×5 open squares centered on the conduit, one around each axis. Only prismarine, dark prismarine, prismarine bricks and sea lantern blocks in the frame contribute to activation. A minimum of 16 blocks are required, and produce an effect range of 32 blocks. Prismarine-type slabs (including double slabs) and stairs cannot be used to activate the conduit.
The effect range of the conduit is 16 blocks for every seven blocks in the frame, though the effect does not activate until the minimum of 16 blocks are included in the build. Thus, it extends to 48 at 21 blocks, 64 at 28 blocks, 80 at 35 blocks, and 96 with a complete frame of 42 blocks. A complete frame also carries the additional advantage of attacking hostile mobs within 8 blocks of the conduit by 4 every 2 seconds, if they are in contact with water or rain.
Other blocks used as part of the frame (including prismarine stairs, slabs, and double slabs) have no effect on activation, and can be omitted. Any blocks outside the frame but within the 5×5×5 cube that encompasses it likewise have no effect.
Best Answer
This is almost certainly a texture resource pack. They're capable of changing how the loading screen is displayed. Click on the third button. This will bring you to the settings screen:
In the General (last) section, the fourth option (at least for me) is Global Resources:
Notice how the Minecraft Texture Pack doesn't have a lock icon on it. Also nothing happens when you click it. You want to disable all other texture packs in the Active Packs section. Do this by clicking on them, then clicking on the - button (which is the left of 4 buttons appearing under the resource pack info). This doesn't delete them, just disables them. After that, it should be back to normal.