In My Humble Opinion, Heather, YOU can fix anything in your computer.
You have replaced a Power Supply, and added a graphics card.
1) The eMachines T5212 Desktop PC uses an Intel D102GGC2 motherboard,http://www.newegg.com/Product/Product.aspx?Item=N82E16813121031
The motherboard supports an LGA 775 processor socket,http://en.wikipedia.org/wiki/LGA_775
Instead of the processor having the contact pins, as in the older Intel Pentium 4 processors (Socket 478), the LGA 775 processor socket has the contact pins.http://www.pcworld.com/product/29441/emachines-t5212.html
After the page fully loads click on the third view down, and the left side.
This inside view shows the black rounded air duct, used on the processor fan.
Here is a replacement Heatsink/Fan combo,http://www.cputopia.com/emachine-fan-t-series-t5212.html
It looks as though the unit comes apart. (unscrews)
If so you can just replace the fan itself.
IF not however, it means the finned aluminum Heatsink, AND fan remove.
In this case you have to THOROUGHLY clean the top of the Processor, and bottom of the Heatsink, and apply Thermal Paste properly.
I can guide you.
[ I know you have been following the proper procedures, but I would hate to learn later that you haven't been, and I didn't post;
Follow Anti-Static Precautions
Your body carries Static electricity. Static WILL fry out (Short Circuit), the delicate hardware components inside a computer.
Relieve your body of Static BEFORE working on your computer, or before taking those parts out of their anti-static bags, or cartons.
Computer on a table, computer Unplugged from power, computer case open;
TOUCH an unpainted surface, of the metal frame of the open computer case.
This action will relieve your body of Static.
IF you leave your computer in the middle of working on it, be SURE to Touch the metal frame again upon your return ]
Be sure to clean in-between the fins of the Heatsink, before installing the new fan.
Know you need to get a new computer?
Only if it fits your needs.
For myself it is internet, Youtube, Adobe Photoshop 7, and office programs.
My Pentium 4 HT, model 540j, (3.2GHz), 2GB's of ram memory, and an ATI Radeon 9250, does just fine.
If you are a gamer, and/or use 3D programs, and/or burn videos, then more 'power' is needed. IMHO.
Windows 7? Windows 8? Yeah, whatever.
I have Win7 on my new laptop.
Perhaps one day Windblows will catch up with Ubuntu and the Compiz windows manager, lol!http://www.youtube.com/watch?v=tRAcskPNof4&feature=related
For additional questions please post in a Comment.
Intel Desktop Board D102GGC2 Product Guide - English (PDF)
= Motherboard manual in PDF file form.
(Adobe Reader uses PDF files)