Power Supply problem, or something else
Lately, when I tried to turn on my pc, it wouldn't happen anything, not even turn on any lights or so on. But after a minute or so, when I pushed the button once again, it would turn on. It worked just fine, no problems at all, I could work with it properly with no problems occuring - this lasted for 3 weeks and some days, I guess. But suddenly, four days ago I tried to turn it on, but wouldn't turn on, not even after 5 minutes or more. I thought this was the Power Supply, so I went to fix it. They changed my Power Supply and it turned on very well. Took it home, turned it on and worked fine. Suddenly, after 20 or 30 minutes, I'm not sure, it turned off itself. I didn't have much time to do anything, becasue it suddenly turned on again. But this time, my monitor didn't turn on. I turned the computer off by holding the power button for three seconds, and then turned it on again, it started but only the green light was on on the computer, the red one wasn't working at all and monitor wasn't on.
What could it be?