"Cleaning up" nested if statements

In a console program I am creating, I have a bit of code that parses through a file. After parsing each line, it is checked for syntax errors. If there is a syntax error, the program then stops reading the file and goes to the next part of the program. The problem is, it is very messy as my only solution to it so far is a series of nested if statements or a line of if statements. The problem with nested ifs is it gets very messy very fast, and a series of if statements has the program testing for several things that don't need to be tested. Heres some sudo code of my problem (note I am NOT using a return statement)

Pseudo code shown instead of real code, as it is very large

Nested if:

open file;
read line;
//Each if is testing something different
//Every error is different
if (line is valid)
{
    read line;
    if (line is valid)
    {
        read line;
        if (line is valid)
        {
            do stuff;
        }
        else
            error;
    }
    else
        error;

}
else
    error;
code that must be reached, even if there was an error;

Non-nested ifs:

bool fail = false;
open file;
read line;
//Each if is testing something different
//Every error is different
if (line is valid)
    read line;
else
{
    error;
    fail = true;
}
if (!error && line is valid)
    read line;
else
{
    error;
fail = true;
}
if (!error && line is valid)
    do stuff;
else
    error;
//Note how error is constantly evaluated, even if it has already found to be false
code that must be reached, even if there was an error;

I have looked at many different sites, but their verdicts differed from my problem. This code does work at runtime, but as you can see it is not very elegant. Is there anyone who has a more readable/efficient approach on my problem? Any help is appreciated :)