COMP KEPT FREEZING WITH A BUZZ SOUND! help appreciated!

Hi All, I have been having this problem recently. My Laptop kept freezing while i was just watching videos on the internet. It usually would happen after i turned it on for awhile and when i am watching the video halfway, it will start to freeze with a buzz sound / freeze with no buzz sound / bsod / black screen with short buzz sound and restart automatically. I am really frustrated about this because i'm afraid that constant holding of the on/off button to shut the comp down will worsen its condition.

And this does not happen only when im watching video. i may be playing a game or just using microsoft word or just surfing the net.
I'm really clueless about this as i'm not really good with computers.So i really hope someone could help me here !! i would really appreciate it!

so after researching online , i did the memtest86 and there wasnt any errors. so i guess its not fault with the ram.

may i know what should i do next?

here are my comp specs

OS: Windows 7 home premium
Processor: Intel Core(TM) i5 CPU M 460 @ 2.53GHz 2.53 GHz
Graphics Card : Intel HD Graphics
Ram :4gb

sorry i'm not really sure what is needed.
BTW the LAptop is 3 years old now and i havent really done anything to it. I did however install windows updates!

Help would be gladly appreciated. thanks guys!!