The problem is that the PC completely shuts off after about 10 minutes of use... when I boot it back up, I get a message saying :-
Alert! Previous shutdown was due to Thermal Event
after i switch the system the motherboard fan work but not in full speed & in the middle of it i could hear some sound like as if its touching any sides & also the fan that's attached to the cabinet isn't working but the fan tht's behind the SMPS runs in full speed.can anyone help in diagnosis what's the problem & how can i overcome it.
The link you posted said it all.
If your fans are making noise or just not working, replace them.
It's very easy to do, it's not as complex as building a machine.