Monitor Randomly Goes Black & Computer Stops Responding?

[James]

I'v got this new gaming computer custom made for me. The specs are
AMD Radeon 7850 2gb
i5 2570k
16gb RAM
500W Power Supply
Win 7
Everything is updated, All the drivers are updated. This has only happened a few days after i'v had this PC. It's happend about four times. Once when I opened up a game, It crashed, I pressed the power button and it didn't turn off, I alt f4 then enter and it didn't turn off. It crashed twice when I was trying to watch this facebook HD video in fullscreen. About halfway through it crashed, And it crashed once when I was just surfing the web ( I was installing guildwars 2 & just browsing facebook) - After an hour it crashed. I took out the HDMI Cables and put them back in. Nothing. I have a feeling it wasn't my cables making the error as when I take the cables out or turn off the PC. It comes up on my monitor (32 inch tv) no signal. When it randomly crash's, it's just black & I don't get the no signal icon. Im using the resolution 1920 x 1080. I'v scanned for virus's with nortan, nothing. It's not over heating as Core Temp.exe ( a program that records the temp of your PC) I get around 29 - 39.
Any ideas? Im stressing over this.
Thanks
When im watching a video and this happends, the sound sometimes repeats. E.g it will repeat 1second of sound over and over again once it's gone black. Only when im watching a video though, It doesn't play the hole video sound, only like a little beep ect.

[sixShOOter50o0]

your computer is custom made. try opening your pc and pushing the RAM sticks in harder and the GPU also. try installing AVAST antivirus and make a system reboot scan of your computer.

that's all.