monitor is going to sleep but the computer is still running

[Raymil]

So my computer is about 4 years old and it works and everything but every now and then my computer will shut off completely for no reason or the monitor will go to sleep and the computer will still run and and i have to hold the power button down to turn it off. And when i reboot it will go to the login screen for my account and then it will go black screen again. Then I have to wait for it to cool down. my computer will get really loud and make like a grinding noise also. I think its the GPU making the sound. the gpu sometimes gets up to like over 90 degrees.anyone know what the issue is?

Specs:
GPU - xfx radeon 5870
CPU - intel i7 930
Ram - OCZ gold 6 gb
PSU - Corsair TX series CMPSU 750W
HD - WD black 1.5 TB 7200 rpm
motherboard - evga e758-a1 3 way sli
cooling - cooler master v8

And I wanna upgrade the GPU, hard drive, and maybe the ram and i was wondering if it is worth or is the motherboard and cpu not that great? thank you.

 

[NarbiusTheGreat]

Woah 90 Degrees (If it's Celsius) is extremely dangerous. Do you ever clean out the dust in your computer? Make sure you do, because dust damages components easily in large amounts. Plus if your computer keeps turning off when it is hot, then it has to be a heat problem with one of your components. Try cleaning it off, my GPU has never even reached 90 degrees celsius even in stress tests. If those problems persist, then there is something wrong with your components or you have a virus. (But it seems you said that it works fine, except it turning off randomly).

Oh my computer is about a month old, and it already has quite a bit of dust in it (Which I cleaned out earlier)

 

[Raymil]

yeah i clean my computer often. i even unscrewed it and there was no dust in it. my fan on my gpu was messing up though. i think that is what is going on. I wanna upgrade my PC tho. should i upgrade the gpu to a 750 TI and the HD to a SSD, and get more RAM? or is my motherboard and cpu too old?

 

[Raymil]

anyone?

 

[Raymil]

Please help.

 

[NarbiusTheGreat]

Hmmph. No dust? So wait your fan is breaking? Then yeah definitely it is the GPU. Your gpu fan must be dead. Sorry to say, but in all likely hood it is your GPU dying. You would likely need to buy a new GPU. But it would be best to check other components before assuming it is the GPU. It could be the motherboard, or the PSU. Does your motherboard have other PCI slots? Connect the gpu into another slot. Check the plugs on the GPU, are they plugged in completely? Is the psu not able to handle the GPU fan for some reason? (It's pretty old). Hope the best for you man, good luck!