Why is my 1998 Honda Accord not starting after tune up?

My neighbors 1998 Honda Accord 4 Cylinder EX needed a tune up and a new radiator hose so I told them I would help them out. The car ran Very poorly ( misfiring vert bad ) and read 6 codes on my OBDII reader. I replaced the Plugs & Wires, Cap & Rotar, but did not do a valve cover gasket because I felt it was not needed. After doing the Tune Up, my OBDII read 0 codes. AND THE CAR STILL WON'T START! I know it is not a power issue, and I am starting to thing it is a fuel issue. The car has a full tank of gas but has been sitting for over a month on a steep incline, so i am not sure if that would affect anything. ANY IDEA'S?

- It ran very poorly before the Tune Up, BUT it did run. And it reads 0 codes and doesn't run… I am very confused on what happened.

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