Crappy Imac Computer?

I have a Imac with 2ghz intel core 2 duo processor and 1gb 667 mhz ddr2 sdram Its a mac os x (leopard).
My question is has any of ya ‘ll have these problem after installing leopard or have these problems period.My imac first thing that happened is that fans or fan stop working(I know because it used to run like a jet engine) then it kept getting severely hot and worse so I got a program to run the fans a little bit faster and check the temperature for it.Well as soon as got it, it said the computer was at 133 Fahrenheit so it worked for a while keeping it between 70 to 110 but after a while my graphics card started glitching up the screen would start flickering and the entire screen would change colors to a mother board look a like color and i had to mash the button to turn it off because I couldn’t figure out where the menus and mouse was to turn it off with the mouse well that’s the beginning of a long roller coaster ride .Then the sound card started messing up on me making a beeping sound well I turned the computer off that worked for a while then a few months later it started doing it again well I did the same old same old except when I turned it off it kept beeping this time I had to unplug it. Well rinse and repeat for a few months. Then I finally took it to a mac store. Only reason why I didn’t do it before I didn’t have any money and I live in the middle of no where the store is like 100 miles from where I live.They ran a diagnostic test and they said they found nothing wrong I don’t think that they looked at nothing at all on the inside.

It’s now worse off then before the fan is slowly getting slower and slower and now I can’t look at a thirty minute video online with out my computer jumping to 122 with my air conditioner on high and pointing at (along with me having snot sickles)and the computer starts off at 90 degrees now and sometime 95.
Can someone give me advise on what to do I’ve got the three year plan. Oh yeah and I had an external hard drive that used work but it doesn’t even work at all it was 500 gb and it had valuable stuff on there.They told me to reformat it which erase every thing and it didn’t even work then and reformat it again for a windows and worked perfectly. All I got is crappy computer that don’t work at all just about it.When I watch a video maybe two ,my computer goes so slow then when you scroll up and down on a web page it actually takes 20 seconds to react maybe longer and then it start scrolling on its own for the time you was scrolling already and the typing is the same. Should I send it to apples main corporation or throw out the door and beat it with a sledge hammer.(might I mention that as soon as you start watching it, it also jumps to the temperature 122 within 2-4 seconds)

I thought that mac’s was better than windows I was wrong plus windows are way cheaper for more and they actually work, or was best buy just selling a piece of crap to me off the bat.