You're going to have to get a second opinion before you declare it DOA, but
I couldn't tell you what to look for myself, although two completely fried
plugs would be a good start.  Any mechanic would have more of an interest in
fixing your car than telling you it's a write-off, so if what your guy told
you is false then he just talked himself out of a major payday.  Doesn't
seem quite right to me, so I'm guessing your mechanic most likely told you
the truth.

If you change your own oil you do not void your waranty (prior claims and
case law supports this), unless of course you changed it at 50,000 miles,
had the mechanic do it at 80,000 miles, then your motor goes south at
110,000 miles before you get around to changing it again.  You still have to
follow the recommended service intervals and keep records, but if you still
have the factory oil filter on the car after 110,000 miles I wouldn't expect
any company would be willing to give you a break. Whomever told you
performing your own service voided your waranty is feeding you a line.

And before you go crying to Kia and telling them what a POS car they sold
you, let's look at the numbers:  This was a 4-year-old car with 110,000
miles on it = 27,500 miles per year (twice the national average of
12,500-15,000), plus at the time it was the absolutely cheapest bottom of
the line car you could buy on the market.  For the work you got out of it,
it appears that you got your money's worth.  I hope you weren't expecting it
to last 10 years with that kind of usage.  I also hope that after you took
your car to your mechanic for routine maintenance that you checked your
guy's work (like pulling the dipstick to make sure the oil wasn't still
black after he charged you for an oil change, looking at the air filter,
etc.).

Good luck and let us know what happens - Jonathan

When was the last time you changed your timing belt?

It sounds to me like you lost the timing belt. Was the engine
exhibiting any signs of distress prior to shutting down? Abnormal
noises, high temp, oil light on? How many miles on the car?

I doubt you could throw three rods without putting a hole in the block
somewhere. Since you have the plugs out the next step would be to
remove the oil filler cap and see if you can look in there and see the
camshaft. If so, put a wrench on the end of the crankshaft and give it
a turn and see if the cam moves with it. If not, you can assume you
lost the timing belt. Since you have an interference engine you will
probably need to remove the cylinder head next and see what is damaged.

Chris