I have old questions that have no answers, and I want to delete them. Is it safe, or will it deduct from my reputation points, or will it be a reason for blocking my account?
Deleting a post will remove all reputation changes caused by it unless the question is 60 days or older and hides it from users under 10k reputation.
However, be aware that deleting too many questions as a new user on that site could cause you to be question-banned. As long as you are in good standing on the site and you have not deleted too many questions, it shouldn't be a problem.
According to Shog9, deleting old questions doesn't have any effect on your chances of getting banned.
The reason why it's bad to delete new questions is because people may be crafting answers when you delete it and it's a bit rude to disallow them from publishing them.
Just because you can delete a question doesn't mean that you should. Deleting unanswered questions is advised against because they could become useful at some point in the future. If someone searching encounters something similar and answers your question after they find the answer, it could be useful to you and other future viewers.
Also, if your question has answers, it's a bit unfair for those who answered it to delete it because it nullifies their contribution.
You really shouldn't delete a question just to delete it. If, for some reason, you are embarrassed by its quality or it is no longer useful to you, you should consider editing it to improve it by adding new information or fixing up the fine details (in fact, by doing this, you're bumping your question back to the top and someone may see it who didn't before and answer it!).