Computer stopped starting up

I have a Gateway desktop computer which is about four years old and it no longer starts up. It used to start up successfully sometimes, but eventually it got worse until the point that it no longer starts up. I heard strange sounds coming from the hardware, as if it were struggling because a part had worn down. When it did start up, it was perfectly fine for hours, and thenit would shut off again after I left it alone for a while.

I was wondering what the problem might be.

 

It could be various different problems ,the most likely is the hard drive or an internal fan has broken and its over heating.

Describe in more detail what happens when you hit the power button,does the hard drive light flicker,does the monitor come on at all.

When was the last time you cleaned the inside?Pull the side off and clean all the fans and heat sinks 'not with a vacuum' and check all the fans are spinning then post back.

 

The light flickers for less than a second but goes out. It always sounded to me like the fan was struggling but I'm not an expert. I'll try that.