Hello ? I have questions about Cooling.
The thing is...We are in the Summer Season.
My computer is Hot because of the summer. My computer is inside of my desk: after 10 min, inside is really hot as usual in the summer season.

Should I buy New case or Should I put my computer outside ?
The thing is ONLY my computer case is really old.
I want my computer become more cooling.

If I should buy the case,
My Motherboard Size is "ATX Form Factor, 12"x 9.6" (30.5cm x 24.5cm)"
Also, I want to keep my power supply. Also, I like cheap and good one that have the best cooling system.

Cooler air in from the front, hot air out from the back is a general guideline.

Hot out from the top is also useful.

Cool in from the side directed at the hard drives and/or the video card card is also useful.

The key is VENTILATION AND AIRFLOW.

So, make sure you have it.

as a thing to see:

http://modtown.co.uk/mt/article2.php?id=blowhole

I did this - 1 - 120 mm fan aimed right at my hard drives and drawing air from behind the motherboard and another in the top right above the cpu heatsink.

If you decide to go new case, this one is a solid and inexpensive case with some nice cooling features (vents and ducts) built-in:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=186336&CatId=1520

I would put the comp outside the desk and also install a second "system" fan. All comps have at least a CPU fan to suck heat off the processor/heatsink. But that hot air builds inside the case. Adding a "system" fan at the upper rear vent will evacuate the hot air out of the case and keep your system cooler overall.

Needs to breath.

If the computer is not giving you any problems at all, and just feels warm, I wouldn't be too worried about it.

Moving motherboards around isn't the most convenient thing to do, and even though I've done it so many times, I really hate doing it. I'd avoid it if possible.

Having your computer running hotter than usual MAY reduce its lifespan, but unless you're thinking of using that computer for the next 20 years or so, I wouldn't worry about its lifespan. Might be cheaper and more cost effective to let it die off, and buy another exact same one in 20 years. I mean, 486s are going for peanuts these days the last time I checked.

Thank you for all replying.
However, anybody know How do I check "Power Supply" ?
Is there any software that show the voltage ?

Yes, use Lavalys EVEREST Home Edition. It's free and gives you every detailed diagnostic information imaginable!