|Most standard sized desktop computer cases, other than some oddball brand name system ones, are designed such that either of both ATX and Micro ATX mboards can be installed in them - mboards in emachines desktop systems are either the standard ATX or micro ATX size.|
If you have a north american model, this page
says this is your mboard - Intel® D101GGC (Grant County) Mainboard (with an emachines bios version) - unofficial info:
You will probably need to look at and abide by the front panel wiring and USB wiring info in that.
NOTE that the mboard has an emachines bios version - DO NOT use a Intel bios update on it, otherwise the mboard may never boot again after you have flashed the bios !!
emachines computers are well known to have el-cheapo power supplies that tend to fail more often than average, and when the power supply fails completely, they are a lot more likely than average to damage something else, often the mboard.
Find the label on the power supply - if the brand is BESTEC. that's the brand most commonly used in emachines systems that has that reputation.
If I were you I would NOT use that power supply - get a case that has a power supply, or get a case with no power supply and get a better power supply.
You can usually replace it with any decent standard sized standard ATX PS with the same capacity or greater.
Standard (PS/2) power supply size - 86mm high, 150mm wide, 140mm deep, or 3 3/8" h x 5 7/8" w x 5 1/2" d , or very close to that, though the depth can be more or less for some PSs.
Don't buy an el-cheapo PS.
See response 3 in this: