Buying a new computer?

Ok so I’m looking for a new computer and I’m not very hardware savvy. My old computer is just that very old so yes anything will be faster. I’m trying to educate myself about dual and quad core then I get information that some programs wont run all core ….well it get beyond me. Do I just look at GHz and be done with it or what…… I’m not a gamer, everything is home/office I do run an older version of auto cad and prepare Power point presentations. Other than that not much more. I would like to get something that won’t be obsolete in a couple of years (yea I know everything is obsolete in a couple of years) but hopefully you get my gist. Any answers?