1)To stream videos you need data pack active on your mobile.
2) Further you can test the speed of your data connection.
3) Streaming videos on 3G network is full of joy, but if we go for 2G network it won't work properly as it consumes more data to stream video, so sometimes it fails to see videos.
4) If you watch videos on YouTube, there is option called Quality, so that you can stream videos in different available formats like 3gp and Mp4
5) If you having problem to stream videos, then you can activate this quality to the 3GP. So that it consumes less data.
6) If it still not work, try to change the network operator.