PC crashes with 1 monitor but not 2 monitors

1 of my pc monitors has died after a while cus it was starting to suck and now my pc crashes with a black screen every once in a while on a youtube video, itunes or a video game but it never did that with 2 monitors, weird huh, I dont know whats up

I also have 6gb of ram and thts in 3: 2gb sticks!

I don't know what the issue is but whenever I use 2 monitors my pc runs fine but with 1 monitor my screen goes black and my system crashes, this happened with both monitors on their own, and no matter what port I connected them to so I'm thinking its my PC thats the problem

its crashed in games, youtube videos, and whilst just surfing the web so its not a program causing it either

Can anyone help me I'd be very grateful

What are the complete specs of this computer? Don't forget to list the motherboard and power supply