paper,
I guess you mean not feeling any particular sensation in your DT (warm etc.)?
From my observations generally there are people who feel it (Qi) quite easy - without any special effort (especially women), and people (like me) who... also were given that gift but under one small condition: "you must help to your success"
So I was, and still I am looking for excercises that help to "feel something".
Those are my suggestions that helped me most:
1. Meditation on DT - you sit/stay/lay down and concentrate
a) put your hands on your DT, you can be rub your hands
b) veery delicate contracting and loosing anus (ring muscle around it)
2. Rubbing hands to make them warm and then rub DT -
for ex. 36x CW and 24x CCW - may be more, perhaphs the more the better (but I'm not sure about that as whole that process
must take some time)
3. Smile to your DT -
every time you do any qigong practice smile to yourself
4. "Smile even more" -
this is very very helpful, maybe the most helpful. Put both hands on DT and...just start laughing aloud. If you do this with other person(s) they help because smiling is infectious (I do not know if this is the best english word). Gently shake your abdomen with your hands while laughing.
(This practice I learned from Mantak Chia's seminars - sorry I know there are sceptics about Master Chia, but I'm not one of them)
5. Do not lose energy (!!!) -
a) very shortly I mean less sex or sex without ejaculation (eg. Healing Love from Mantak as well, unless there is any teaching about that from Master Yang - unfortunatelly I do not know that)
b) work less, rest more
c) keep warm and healthy
d) check your diet
6. Massage DT and kidney
Those are some quite easy and safe excercises, and are main techniques that helpled me the most.
Personally I do not recommend you doing reverse breathing techniques unless you are under really good and experienced teacher.
All that process of gathering Qi in lower Dan Tian is called "Warming the Stove", it must take time, so be patient, keep the faith and practice.