PC case? Standard atx or micro atx?

Looking at the images for your PC the case looks to be ATX-ish - ie it's bigger than an micro atx.

Here's the issue though… When you buy from a company with the buying power of Lenovo you sometimes find that the components are non-standard. Looking at the motherboard for your PC and looking at a standard ATX motherboard, it looks very similar, but not quite identical! My suspicion is that a replacement motherboard would not mount in your existing case, and it may well be that the PSU is also non-standard!