Jesus never said personally that his mother was a Virgin, but the original accounts report that Joseph found her to be such, and was, in fact, going to divorce her for infidelity until he heard from an angel that she was still a virgin. Seeing as how it's pretty easy to prove somebody's a virgin just by looking at their 'parts' (barring some sort of accident), he would have found out if it was true or not and would have acted accordingly.
As far as the theory that Jesus didn't actually die on the cross, that's fallacy. Jesus was stabbed...in the HEART...with a spear before they took him down. He was also locked in a tomb with no food or water for 3 days, and anyone who has bled that much cannot survive three days without water.
Jesus also stated before the Sanhedrin, to a very direct question, that he was, in fact, the living, breathing, one and only son of the living God. The "sons of God" metaphor doesn't apply in this case, as it wasn't used back then and any similar statement would be considered blasphemy, one of the crimes he was charged with.
If you'd like more detailed answers than I can provide, there's a book called "A Case for Faith," by Lee Strobel. I haven't read it, myself, but it's written by a former atheist and makes a very compelling factual case to support the factual existence of Jesus and the factual events that occurred during his life. I've heard nothing but good things about this book.