Why isn't my new ram playing nice with my old ram??

Without spending the time to look up the detailed specs of each, I would assume that the BIOS settings each needs are to different from each other for them to work together.

Unless you're very familiar with ram settings I doubt you'll ever get them to work together.
And even than they would probably have to run much slower than their specs.

That's why memory is sold in "matched" sets.

And, no, just buying another set of the same memory (either one) has little likelihood of working either. Even though the "advertized" specs may be the same, the complete specification can be (and likely would be) to different also.

A lot depends on the motherboard with this too.

Mixing sets of RAM can work (though they'll all need to run @ the lower spec as mentioned; voltages are also a big issue).
However while it might turn out fine on one board, it could be a complete disaster on another. This is why matched sets are always recommended.

Both of those kits appear to have the same specs (1333MHz / CAS 9 / 1.5v, though specific timings weren't mentioned on the Wintec kit).
What I'd do is remove the set you already know worked fine, and see how the new G.Skill kit does on it's own in your board.

Some kits just don't play nice at all on some boards, this is why board makers will usually list tested / approved kits on their product pages.