When you keep showing up and nothing moves
A prayer offered while you feel nothing is still a prayer, and it still counts. The Qur'an treats the condition of the heart as a real thing with its own weather: hearts that grow humble at the mention of God, hearts that harden after long years, hearts with something settled over them like rust. Noticing the numbness and minding it is already a form of attention.
What people usually mean by feeling nothing is that the words arrive on time and the attention does not. You stand, you recite, you give the salam, and the whole prayer has gone by somewhere behind you. The Qur'an puts that gap to believers as a question: "Has the time not come for those who believe that their hearts should grow humble at the remembrance of God". It is addressed to people who were already praying, about what a long stretch of ordinary years does to a heart.
Hardness, in the Qur'an, is a condition, and conditions move. The image it reaches for is stone, and it does not leave stone as the last word: "there are stones from which rivers burst forth". A heart that has gone quiet is being described, and described as something water can still come out of.
The Qur'an also describes what feeling looks like when it does come, and it comes in an order: awe first, then softening — "then their skins and their hearts soften at the remembrance of God". Softening follows the standing and the listening, which is worth knowing on a day when you are trying to summon it in advance and finding nothing there.
Presence is the part you can work on: slowing the recitation until the words have room, praying nearer the start of its window than the end, keeping a little remembrance in the hours between prayers, and using the quiet of the night, which the Qur'an says leaves a deeper imprint. The condition named for a reminder to land is someone who "listens attentively and is present", and presence is something you can give on a day when you feel nothing.
Numbness in prayer describes a season, and seasons are the ordinary material of a life with God. Keeping the appointment while the feeling is missing is its own kind of faithfulness. More on the shape of the prayer itself is in Quran verses about prayer; if the quiet is wider than prayer, Quran verses about feeling distant from God sits closer to it.