Hi If the oak has gone black it is unlikely you will get it back. Allow it to dry out fully then sand the surface and see if it gets paler underneath. Depending on what the original floor finish is will depend on whether you need to re sand the whole floor to achieve a uniform colour. However as a temporary measure, dry it out, sand it back and re-seal with either a uv matt varnish or a hardwax oil. Follow the instructions on the product tin. Back to the black... Oak has tannins which react with water and turn the timber black. This can seep down through the whole plank( you see it most often on worktops around the taps). If this is the case you will be better getting in a joiner/ floor fitter to replace these areas. Good luck

It looks like plasterboard and artex. You’d be better off with tiles. You’d never have to touch them again.

You probably have water on the brickwork outside which is causing this. So you need to remove the cause of the problem. Clear the gutters, make sure the drain isn’t blocked, have any broken flashing fixed, dig away and earth mounded against the porch above the damp proof layer, remove any conifers that could be directing rain run off onto the brickwork and check to see if the brickwork outside needs repointing.

Try IKEA Schottis blinds. They’re about 1m wide so you’d need several to go across your window. The black ones are fully blackout, the white ones aren’t. Best thing is they only cost £5. We used them in our bedroom when we were decorating/refurbishing. Worked a treat. They stick on with tape at the top - we used a bit of blue tac at the bottom.