Ac cords or power conditioning first?

On all applications I know about outside of audio (where instruments are used to verify effect), it is dedicated lines & power conditioning, period. That is the way I went for noise control on a wide variety of industrial equipment and for my home stereo.I never was able to detect any improvement from different power cords. Will not debate pc's with others, just my experience fwiw.
If you plan to eventually use a power conditioner I expect that you will want/need a minimum number of outlets and will be plugging several components directly into the pc. I'm running my system with a total of 4 outlets & I've got several components. It is nice to figure out a place to plug the non-sound garbage generators (e.g. turntable drives & etc.) that is not on your dedicated line.
Good Luck!

Don't forget the audiophile grade duplex covers as well.

There are a lot of different approaches to this and dedicated lines are a good first step. However, you may still need to follow that up with some type of line conditioning depending on the environment you're in. Take a look at Alan Maher's products. These were the last stop for me in my efforts to clean up power and address EMI/RFI:

Alan Maher Designs

Go to the local wholesale electric store get two two receptacle boxes, four hospital grade receptacles, two hospital grade plugs the appropriate amount of the best 12/3 cord they have and make two extension cords for eight plugs. Next throw the monster power strip in the trash, then with the money you've saved buy some isolation devices for your equipment (sorbagel from E-Bay) etc!!!

What is approach if you can't do dedicated lines. I live in a 1953 all stone house, running wire is impossible, (the walls are stone block).