|OK, if you had said that to start then the answers would have been different.|
I can't find any information on what form factor your motherboard is. I am not sure you can install that motherboard into an mATX or ATX case. The power supply will be too small to power much of a graphics card either.
So, you may be talking about a case, power supply, motherboard.
Might as well sell that rig and get something that will do what you need.
Your small computer may have some resale value if you keep it intact.
Below is a link to the specs of your computer. Can't determine the power supply ratings but that type of computer are usually under 200W.
Look at the link below to determine what form factor ;your motherboard is. You need to measure it.