To save some time: I don't know the exact year model, nor the exact engine (although I'm fairly certain that it's a 2.2, because the base models have the black bumpers and the others don't, and this one has them.). It is my friend's aunt's car who plans to sell it to a salvage yard. She has a maximum offer of $300 from a salvage yard, and she'll sell it to me if I can match that price.
The way she described the problem and the steps (which lead to more problems) to solve it is ambiguous, so please try to bear with me.
She had a leaky injector, boyfriend looked at it, took it out to check the O-ring, O-ring was fine, he replaced it, then the car wouldn't start. Boyfriend took out all of the spark plugs and spark plug wires at the same time (don't know why he did that >

), air filter, oil pan, alternator, what looks like the water pump, and some more stuff... Oil now has gas in it.
First of all, I'd like to find the reason as to why the car might not start after taking out, inspecting, and replacing an injector. Google didn't seem to have the answer, so I'm asking here.
Any help is greatly appreciated. I apologize for the vagueness. The woman isn't very technical and all of the work was left to her unattended boyfriend.
Thanks in advance.