My thinkcentre S50 is broken, help on upgrade/fix please?

So the motherboard in my thinkcentre is broken, so i'm thinking what kind of mobo should i buy (itx or what)? And will any mobo of the right size do or will i need a specific one? Thank you!

Added (1). P.S. I've built PC's before, and want to make this into a light use HTPC for some videos and film watching, e-mail and internet browsing(for mum) and minecraft (little brother).

Added (2). P.P.S. Is it worth repairing it, or should i sell it for parts, and build a custom HTPC… Muahahahahaha…