My pc never use to over heat even when i let is run for days but now after i installed a new GFX card (Nvidia 8500GT)it over heats in 5 hours and turns off even when i'm not palying any games. When i turn it on it beeps and a Bios message says due to thermal issues it had to turn off. So how should i fix this problem and by the way my GFX card has its own fan to cool it, cpu has its own fan, another fan in the front and one for the power supply (420watts)

It would help if you listed the case & CPU temps...both at idle & under load. Average room temp would be helpful as well. That would give us an idea of what's going on.

The 8500GT isn't powerful card so it seems unlikely it would add very much heat to the case, unless your case is poorly cooled to begin with? What video card were you using prior to the 8500GT?

Do you have an exhaust fan in the rear of the case??

I do have a exhaust fan at the rear of the case, i was using the intergrated GFX card on my mother board prior to the 8500GT, the case is ATX mid tower caes , room temp is 23oC/80oF, CPU temps:Processor zone=96oC/204oF, System 1 zone=67oc/152oF, System 2 zone=66oC/150oF. Processor fan speed 3199 RPM, Rear fan speed 2589RPM, Front Fan Speed 0 RPM, i think my front fan just died and thats why its heating up maybe because its showing front fan speed 0 RPM on the bios. so please let me if i should change the front fan??

Are you sure those temp readings are accurate? Generally speaking, the system temp should be no more than 10C +/- higher than the room temp, & the CPU temp (at idle) should be no more than 10C +/- higher than the system temp. Your temps seem WAY out of whack.

That means with a room temp of 23C, your system temp should be roughly 33C & CPU temp roughly 43C. I doubt the front case fan has anything to do with your problem. I realize that this is an Intel system, but the AMD Builder's guide states that a front intake fan is virtually useless. I don't see why Intel's cooling requirements would be significantly different than AMD's.

Try temporarily removing the side panel from the case & monitor the temps & if possible, position a small room fan so it blows directly into the case. Then try playing a game or you could run a stress program such as SP2004 (Stress Prime 2004) or TOAST to really max the temps.

Front fans for the most part doesn't do much on ATX motherboards, Unlike it does on a BTX motherboard, but that's another story altogether.

Yes those readings are acurate and i have some new reading which i took right after my pc turned off when i was playing a game
CPU = 105oC
System 1 = 75oc
system 2 = 77oC
This is the temp i recorded after 2 or 3 mins when my pc tured off
room temp is 21oC whith A/C on
Then i did what u said "Try temporarily removing the side panel from the case & monitor the temps & if possible, position a small room fan so it blows directly into the case. Then try playing a game or you could run a stress program such as SP2004 (Stress Prime 2004) or TOAST to really max the temps." with this i tried 3 games (Bioshock, GRAW 2, Cricket 07) and my pc never turned off and the temp reading were at CPU = 79oC,
Sys 1 = 40oC
Sys 2 = 43oC
so what should i do??
Another question is that: is the rear fan suppose to bring air in or blow the air outside because the rear fan seems to be bringing that air in side if thats the case should i reposition the fan so it blows the air out(flip the fan)?? Also the cpu fan is sucking air and blowing it into the cpu.
Also my cpu fan is really dusty should i clean it??

Rear fans should ALWAYS blow outward. Side fans should not be used because they disrupt the front-to-rear airflow.

ok so i have flipped the rear fan so its blowing air outside and my cpu fan is sucking air and blowing it into the cpu.
Also my cpu fan is really dusty should i clean it??

"Also my cpu fan is really dusty should i clean it??"

Definitely! And try to clean between the "fins" on the heatsink too. Do NOT use a vacuum though because it can cause static that can damage electrical components. Instead, use a can of compressed air (about $5) to blow the dust out. If you're very careful, a small soft bristle brush will help loosen the dust. Make sure to unplug the power cord before working inside the case. Afterward, you can vacuum the floor...lol.

I clean the insides of my PCs with compressed air about once a month.