My son is almost 2 and he used to sleep straight through the night from 7:30pm to about 5am up until about 6 moths ago, he now goes to bet at 7:30pm and wakes up at about 12am and then calls for me or his dad and hen we struggle to get him to sleep again. He is in his own bed in his own room so its difficult to try and let him cry himself to sleep if he can get out of his bed and come to our room. Please help me!!

Have you tried music, we gave my niece her own cd player that she could turn on if she couldn't sleep. Every kid is different, but with her we went about it by saying, We are going to give you something special, but you have to stay in your room at night to get it and if you want to keep it you have to stay in your room. We did a similar thing with her sister, we told her if she stayed in her room all night we would make her muffins. I bought mini muffin tins and those were all for her(she loves food). She once went and sat on the stairs cause she couldn't sleep. Her mom woke up and found her asleep on the bottom step. So cute! She was then informed that she could wake up Mom if she was sick or hurting. She said "I was not. Just not tired."
Good luck with your son, I am up with mine now, he is just under 2 months. :)

Martene, hi, does your take a nap in the day? Or can you have him go to bed at 8 instead? A night time routine is always good, and a few words about staying where he should are good too, like the above poster said.
If he takes a nap, cut it short or take it out of the picture, a good nights sleep is imperative compared to a good nap. If he doesn't nap then you can start a nightly routine, you can bathe him, give him a snack, read a book then tell him it is time for bed, no ifs and s or buts... ;) Oh I know it is easier said than done. I know because we had this issue with three out of our four kids. When he calls for dad, one of you go in and tell him we are sleeping, you need to go back to sleep too, kiss him and leave his room...
You may have to do this a few times in one night and then another, but slowly he will stop calling and it will be over. Good luck!