Something Wrong with my Dell Dimension 8 ...

last week around thursday my computer was kinda turning off on itself, The monitor would be blank but the computer would still be on(its not a monitor problem) Then on saturday my computer just shut off completly and when i try to turn it back on it would turn off immediatly. I would the power button like 5 times and it would turn off in a second. Then sometimes it would turn on but the fan sounded really low usally it is slightly light not extremly loud but i would be able to hear it but now it was just to silent. Though it was on no image was on the monitor and then the computer would just off. I opened up the Computer try to smell if anything was burned but didnt smell anything. I also cleaned out all the dust. The power button would normally be green but now its turns orange sometimes. It would be orange at one time i turn the computer on or green when i turn the computer on. Then just yesterday i got it to turn on it went all the way to the sign in screen and i signed in the it shut down. Also the motherboard light is green so i would assume there is nothing wrong with the motherboard.Something Wrong with my Dell Dimension 8 ...
2 obvious thing,1) Your PSU is packing in, not supplying the right volts to the rails2) The thermal paste on your CPU has burnt away causing the CPU to overheat and activating the automatic CPU shutdown...