Here is my computer stat if that might help you (btw, heat problem on idle would be a little weird, but you'll understand fast that it isn't a problem lol).
CPU: AMD Sempron 3100+ (new)
Motherboard: GA-K8NS PRO (new)
PSU: Ultra X-Connect 500w modular (new)
VGA: XFX GeForce 6800 GT (new)
Memory: 3x 512 megs DDR PC3100
Hard Disk: 1x Maxtor 200 gig
1x Seagate 200 gig
CD-Burner: Plexwriter Premium
DVD-Burner: LG dl 4x
Case: Thermaltake Armor Case Aluminium (new)
Cooling: Thermaltake Big Water Cooling + VGA Water Block (GPU at 51 at high load, cpu at 39 at high load, celcius) + 3 120mm fan (2 on radiator on the back, 1 intake in the hd case) + 1 80mm top of radiator + 1 80mm on top of case (new)
So as you can see, the cooling factor isn't a problem lol. By the way, except for the pieces said as new, all other have less then a year of usage and always worked great in my last computer.
I also have a problem reading my backup cd's, they don't read into my dvd or cd burner, but they read in any other computer (and work with my dvd/cd burner into another computer) and I can't extract topology like I used to. I think it's a motherboard issue, but it make 2 times I change it (first time, water cooling leaked on it on 1rst boot... computer never booted, had to change it... but this time, it never leaked and isn't leaking).
Thanks for the help but I think we need to check another thing lol.
I've tried running memtest86 and a ram tester from M$, both ran without any error. I also did 3 cpu tester (with heat test, crc check and all), all ran fine (ran for 8 hours). I'm out of ideas! lol