There is a profound honesty in that question, and I wonder if it might help to know that not knowing how to pray is, in itself, a kind of prayer. When the words fail and the mind feels clouded, you are not necessarily doing something wrong; you may be entering a space where God is working in a way that bypasses your usual efforts.
St. John of the Cross speaks directly to this experience of feeling unable to lift your mind or heart to God, describing it not as a failure but as a specific kind of divine work:
> "But there is here another thing that afflicts and disconsolates the soul greatly, and it is that, as this dark night has its faculties and affections impeded, it can neither lift affection nor mind to God, nor can it pray to him, seeming to it, as Jeremiah says, that God has placed a cloud before it so that prayer may not pass through. [...] And if sometimes it prays, it is so without strength and without savor that it seems to it that God neither hears it nor cares for it. [...] Truly, this is not a time to speak with God, but to put, as Jeremiah says, its mouth in the dust, if perhaps some actual hope should come to it, suffering its purgation with patience. God is the one who here is passively doing the work in the soul; therefore it can do nothing" [4].
When you feel you cannot pray, perhaps you are simply being invited to "put your mouth in the dust" and wait. In that stillness, where your own activity ceases, God is secretly at work in the depths of your soul, even when you cannot sense it or formulate a single coherent thought. You do not need to produce feelings or words to be heard; your patient presence in that darkness is enough.
Thomas à Kempis also offers a gentle reassurance for when we feel distant or unable to find the right way to turn to God, reminding us that His nearness is not dependent on our eloquence or our sense of connection:
> "Son, I am the Lord who strengthens you in the day of tribulation. Come to me when things are not going well for you. [...] Do not think yourself completely abandoned, even though I have permitted some tribulation to come upon you for a time; for this is the way to the kingdom of heaven. [...] When you think yourself farthest from me, I am often nearest to you. When you think all is lost, then the opportunity for gaining merit often draws near" [1].
You might try simply showing up in that feeling of "not knowing," trusting that your desire to reach out is itself the prayer, and that the One you seek is already holding you in the silence where words cannot go.