Computer shuts off while watching video

[Tuna425]

I have an HP Pavilion HPE h8-1214 Desktop
The only changes I made to the unit is to add a 130GB SSD and a Ceton tuner card.
Everything else is stock
The problem I am having is if I watch a video in Media Center or online the computer will turn off.
I don't mean shut down. I mean it acts like someone puled the plug. I have to press the power button to turn it back on.
Now I can have the computer on for days without a problem. I can watch video using VLC or Windows Media player But as soon as I try to watch something in Media Center or an online video it turns off.

Any ideas?

 

[Randycool79]

How much memory do you have? Memory could be the problem because you need enough memory for those programs to run

 

[Tuna425]

10GB

I've been running this machine for over a year without any changes