There are 2 instances when you cannot seem to feel Reiki:
1. You have never felt Reiki, even after attunement.
There are a percentage of people that will not feel or hardly feel any sensations on their hands even after being attuned to Reiki. Rest assured, this is ok as Reiki is still flowing through you regardless whether you 'feel' it or not. Sometimes it takes a longer time before you feel it. Some people are not naturally sensitive to energies. If you have this issue, you can still see the effectiveness of Reiki through the resultant effects of the healing on yourself or the recipient. And that is perhaps more important. Trust that Reiki is still working through you.
2. The sensations of Reiki have dissappeared or hard to feel on your hands, unlike the strong sensations in the past. This symptom of "no feeling" is also normal. We have all experienced this before in different ways. Even me.
Of course you are still fully connected to Reiki energy and perfectly able to channel Reiki, even if you are not feeling it right now. Sometimes we tend to put pressure on our selves to "perform", meaning we MUST feel Reiki or else there is something wrong. This is not the case. What happens sometimes is that we are trying too hard to channel Reiki in a certain way and by forcing an expectation, we actually block the experience by being stressed in our body and our minds. The solution is to slow down, release all expectations of how we should be feeling Reiki each time we channel it. Some days our sensitivity is low, some days we are highly sensitive, our body is organic and so it also goes through transitional periods. So let the experience with Reiki advance and change in its own way.
You can of course take a break for a short time, and come back when you are ready and positive again. Be gentle with yourself, allow Reiki to show itself as you use it. The more you channel the more sensitive you become. Each time you channel Reiki make a point to relax completely and just KNOW the healing energy is pouring through. RELAX RELAX RELAX. Once your body and mind are fully relaxed and filled with trust that Reiki is flowing through, the feeling will return by itself. I also recommend you practice re-attuning yourself too if you are a Master or go get a Reiki Booster session, this often also increases the feeling again.
There is also one more reason why you can't feel it right now. If you have been heavily using Reiki, your body might have now become used to the vibration of this energy and so you nullify the feeling as your body has already been attuned to that vibration. You can only feel a vibration if it is of a different vibration from yourself. But as you continue using Reiki, your vibration will again start to ascend, and you will start to feel a higher vibration after you transit through this plateau. Keep using Reiki, it's always there, regardless of any physical sensations you think you 'should' feel.