It is impossible to have an omnipotent, (all powerful) omniscient (all knowing) god.
If your god is omniscient, then he knows everything that has happened and that ever will happen. But if he knows what will happen then he cannot change it, therefore he cannot be omnipotent.
But if he decides to change some future event, then he cannot be omniscient because he did not know the new future before he changed it.
Logic completely destroys god at every turn. It's just so easy. If you ignore logic then you ignore reason and can consider yourself to be willfully ignorant or blatantly irrational.
--- further exploration ---
Actually, it turns out that omnipotence is a problem all by itself. Go ahead and read about the Omnipotence Paradox on your own.
In general, the religious believer's argument to the paradox goes something like this, "Yeah okay, there are some things that god cannot do, but he is omnipotent anyway. Nah nah."
Davo