I was talking to my friend with jumblo and when i cut the call and opened video on youtube but i couldnt hear the sound. how can i resolve dis problem

Hello,
Try updating your flash player. Go to adobe.com and look for adobe flash and install it. It's for free.
You can also check your volume settings. Maybe it's muted or it was changed. Also, check youtube's audio controller to check if it's full or not.
If everything seems fine, then I suggest that you update the drivers in your computer. Drivers are small software which make the parts of your computer to communicate with the operating system. If they are outdated then the parts will stop working.
You can use RadarSync to scan your computer so that you will know which ones are outdated and you can use the same software to update them all.

I hope this helps!

David