99 CV P71 will not turn over

I've had this 1999 CV P71 for 8 years. 180K
Has never failed to start - EVER!

Few days back I got an oil change. Offering $20 oil changes 5w30 (ok sure).. So I got an oil change - I'm only mentioning that because the starting issues started almost immediately after that.

Finally it just stopped turning over at all.
Battery good, starter is cranking.

So - I replaced all my spark plugs. They haven't been changed in 6-7 years anyway; and they did in fact need it. Still won't start.

Any info would be of help. Thanks!

EX-PI

I guess some clarification is needed. You say stopped turning over and you say starter is cranking, can't have both. Is the starter turning and cranking the engine in a normal manner? Or is it slow or non-existent? Is it turning great but the engine has no indication of spark or starting?

The car is cranking it's just not starting.
This is accurate:
'Is it turning great but the engine has no indication of spark or starting?'

An engine needs 3 things to run. Fuel, air and ignition. Most always it is getting air so we'll skip that. A quick check if it is a fuel problem is to use a starting fluid spray. If it causes a attempt at start then fuel system problems would be traced. If not, then more than likely it is ignition. First I would see if spark plugs are sparking. If so, then they may not be doing so at the correct timing. Unfortunately there are hundreds of things that can cause an engine to not start. I can only give you a couple of starting points to begin your search.

I sprayed starter fluid into the carb today while cranking the CV; once without the accelerator and once while applying gas with the throttle plate open. It didn't even act like it was thinking about starting. Back to the drawing board.

8/5/16
Starting problem resolved.
I replaced the fuel filter under the passenger back door. Done. Started right up.
Thanks all!