computer may be overheating

Hello.
I know nothing about technical things. I have noticed that there is a round area in the back of my desktop pc, which has circular bands and lots of room for air. I thought it was where my fan is located, but when I opened the computer the black fan was close to it, but a large metal box was behind the round area. It said Dell on the top and a model #, and 'caution, hazardous area'. I don't know if a fan was inside this metal box or not, but when I'd put my hand over the outer round area it felt warm, and has felt that way for a while. I cleaned the visible black fan as best I could, and where I could on the inside without touching any of the motherboard, ect, of course, then closed it up. When I'd first opened it I could feel the heat in the inside of the computer. Is there a fan in the metal box, if so how to clean it? Any ideas as to what is going on with my computer that is causing it to be warm? Even I know this isn't right. The computer has been slow for a good while. I have deleted many old programs and bits of uninstalled programs, run two cleaning programs, a disk and automatic file fix check, emptied out everything possible cache wise, so on. It is free of malware. I don't know what else to do, appreciate any help. It is a Dell optiplex gx110 running on xp prof, serpack2. It has a memory upgrade and has total windows memory of 1759 mb, intell pent. 3 processor of 933 mhz.I just have a dial-up connection.
Sheena

 

Please post the model name/number (example: Optiplex GX270) and the style of case (tower or mini-desktop). This will help us figure out how the fan is configured on your PC. Thanks.

 

If this is your case, the metal box is your power supply and the only fan in the case by the looks of it.



Which of the figures here are your case?

http://support.dell.com/support/edocs/systems/opgx110/ens/ug/inside.htm#internal_views

 

Well, gman and tgell, this time one of my computer questions may still be a challenge to you. As I said in my first post, my computer is a Dell optiplex, gx 110. I have the monitor sitting on the tower, which is a rectangle shape on my desk. In that configuration, the tower on its side as a rectangle is 4" high, 15.5"wide, and 18" long. I went to the Dell site, thanks for the link, tgell, and while the larger towers looked alot like mine on the inside, NONE were identical. In the picture you posted Tgell, right next to figure 11, the power supply box, just to the right back of the power supply box, inside my computer, is a little black fan! That is the fan I mentioned that I cleaned in my post. It is about 3" in diameter and I did not see this part on any of the dell machines. So how bout that?

 

It's a case cooling fan
http://www.ecrater.com/p/10340356/dell-optiplex-gx1-gx1p-gx110
I have one inside my very old, Optiplex GX1 (700MHz).