Depending on how the contest is run, it could fall under the laws of your State or Country regarding sweepstakes and/or lotteries and/or gambling. Those laws vary from state to state in the US and from country to country.
Generally, you can give stuff away as long as there is no fee, or purchase necessary to be entered into the giveaway. You can ask for email addresses (to be notified) or joining of newsletters and such, but you cannot require people to spend any money, entrance fees, purchase anything, CC numbers, or anything similar to that. As was mentioned, laws vary from state to state...some states don't allow you to give away certain items such as anything that promotes liquor, smoking, gambling and so on. You are usually O.K. giving away [legal] music downloads, gift certificates, CD's, some electronics, tickets...harmless stuff like that. I run contest all the time, winners are picked at random from subscribers, facebook friends, and twitter followers and I give away anything from CD's, and Event tickets to DJ equip and other electronics.
Thanks for the info. I want to have 2 contents. One for the most popular music video and the other is about the latest apps.
It really depends on kind of prizes you give and on what kind of contest it is. There's no problem on running 2 contests at the same time, you could even be running 20. It just depends on how you do them
There are not that many lawyers here at DP that I have read about. The question is way too broad in scope to answer. You have to give more detail as to your intention. There is no earthly way to paint this picture with a single brush. The general answer is the same as with all online pursuits. That is; Play it out until someone says you are breaking the law. Then cease and desist. Or you can fight it out and see what happens. That is the wild-wild west answer. I am sure there would be much research required to give a reputable comment here.