OMG!!!!!! my imac keeps turning itself off???

[joeysteel]

I went away for three days and left my imac on....then after i installed the security update, then my mac started going nuts. The screen just went black... i could still hear the hard drive and the components running but it was still black.... so i did not panic....turned it off and left it to chill.......then turned it back on....1st time i turned it back on it was still black, 2nd time the white screen came but then nothing happened for like... ever, 3rd time it started as normal loaded even... then catastrophe it went black again....i do not know what to do.....i have resorted to using my windows laptop....i am hating this...

please help me

[purelithium]

When you boot, hold down the Apple+V button, and let us know what you see on the screen before it "goes black" if you see anything at all.

I have a hunch that your video chipset has failed.

[joeysteel]

I did as u asked and held down the apple +v and I got a whole load of writing the problem is still occuring it frustrating as it will not stay on for more than 10mins

[purelithium]

I know you got a lot of writing, what were the last say 10 lines? Did the screen go black or did it just hang there with writing?

How old is your imac? do you still have warranty?

[joeysteel]

after the writing it continues to load normally then shuts down, the screen goes black but i can still hear it on.... i will try and get what the last 10lines