Okay so generic case then.
Well seeing what you have here it may be in your best interest to get a new machine, that is if you dont feel you can build one on your own.
Your hardware is quite old, upgrading the processor is not going to do and i dont think adding things like RAM will help too much.
As a gaming machine this is sadly past its prime, now if you made it into some sort of home theater PC that would be fine but games will only begin to get worse from this time forward.
The only reason why I wanted to see the case is to see if there was a way to mod it for more modern hardware but its not going to do a lot of good.
The only parts worth saving from this are the hard drive and the optical drive and the latter almost being rendered useless on more modern computer cases.
Its got a no name brand PSU too so there is not much to do here.
I mean yeah it sucks but it happens, games like DOTA 2 can be very intensive these days.
I mean you could make this a linux machine it will be wonderful but as a gaming rig alas.