Brown line in the middle of one of my nails and half of the nail is brittle, could it be fungus or nail damage?

Splinter hemorrhage. Splinter hemorrhage can be from a trauma but may be a sign of lupus erythematosus, psoriasis, an infection of the heart valve (endocarditis). Brittle nails can be caused by vitamin B7 (biotin) deficiency, a thyroid problem or a fungal infection.