First of all, treat the fever. Get antibiotics and antipyretucs like paracetamol for him. Get a workup, like dengue, typhoid, malaria, cultures etc. He will get a little better. Later, plan a lumbar puncture as a first step for NPH(if that's the diagnosis). This will include draining the fluid bedside. And the improvements in walking is seen after the tap. Then, we plan further treatment.