Perhaps still a bit rough and unpolished, but here the argument is anyway:

1. In every prior state of reality something existed.
   1. Something exists.
   2. If (1) and there has not always been something, then something began to exist uncaused.
   3. It is impossible that something began to exist uncaused.
   4. Therefore, it is false that there has not always been something.
2. In every prior state of reality something existed with the ability to cause.
   1. There are things with causal power.
   2. If (1) and there has not always been something with causal power, then something with causal power began to exist without a cause.
   3. It is impossible that something with causal power began to exist without a cause.
   4. Therefore, it is false that there has not always been something with causal power.
3. The simplest explanation of something is probably true.
4. The simplest explanation of (1) and (2) is that there is one being that existed in all prior states and had causal power in all prior states.
5. It is impossible that a past eternal being is caused.
6. There are caused beings.
7. The simplest explanation of (6), given the previous steps, is that all caused beings are ultimately caused by one uncaused being that existed in all prior states and had causal power in all prior states.
8. Therefore, there probably is a single past eternal uncaused being eternally with causal power that ultimately caused all caused beings.