This Gateway GT5228 Media Center desktop computer?
http://support.gateway.com/s/PC/R/1009153/1009153nv.shtml
(Gateway.com/Support/Documents/ page)
Specifications page,
http://support.gateway.com/s/PC/R/1009153/1009153sp2.shtml
You have an AMD Athlon 64 X2 4200+ processor.
This means it's a motherboard that supports AMD processors, and the Athlon dual core model.
http://en.wikipedia.org/wiki/List_of_AMD_Athlon_64_X2_microprocessors#Athlon_64_X2
Yes, I'll bet it's 'Tricky'! Information I can find, indicates it's a BTX form factor motherboard.
The usual form factor for computers is an ATX form factor, or Micro-ATX form factor.
http://en.wikipedia.org/wiki/Motherboard_form_factor
The BTX design, (Form Factor) places everything in a different spot, than the usual ATX, or Micro-ATX design. The I/O shield is in a different place, as well as (Usually, NOT always!) ,the power supply placement.
(I/O shield is the thin piece of metal in the back of the computer. It surrounds the I/O ports. I/O stands for Input/Output. Examples of I/O ports, are the keyboard, and mouse port)
I would buy a cheap computer case, and a decent motherboard that your Athlon 64 X2 4200+ processor will fit on. (And work!) Plus another power supply. You can reuse your ram. But if I were you, I wouldn't want to! Read on! (Yeah, I know! Almost another computer! You can reuse your optical drives! Sheesh! lol!)
Lucky you! AMD parts are cheaper than Intel parts!
Here is a couple of suggestions for a computer case, motherboard, and ram, plus power supply.
1.Case:
A.http://www.tigerdirect.com/applications/category/category_tlc.asp?CatId=1847 Any of the cases from $50 to $80 bucks will do. Choice is yours. DO NOT trust the power supply's!!
Cases are okay, power supply's are NOT!
2.Motherboard:
B.http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3581158&CatId=2320
The above is pretty close to your old motherboard, except it's not a BTX design. It's a piece of junk too! (No slam to you!)
C.http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3939759&CatId=2320
Something like this, is a Whole lot better!
3.Ram:
D.http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2206874&sku=C13-2022
Recommend the above (2GB's of DDR2 at 800MHz), or this, (4GB's of DDR2 at 800MHz)
E.http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3228139&sku=C13-6082
4.Power Supply:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3276573&sku=ULT-LSP650