Help! Engine derated to 25% and won’t start!

[imalumberjack]

I googled it sooo this is not from experience, its what I found online and seems reasonable.
1761 seems to be ; DEF tank level sensor circuit sensor failed (high). Did you disconnect the sensor? and forget to put it back?

I do not think it would prevent truck from starting? You might want to change DEF filter while your working on it ....if you ran tank dry? everything in there went into filter.

The reason I did not address other codes as they are somewhat irrelevant, often with these engines they will give you info but you need to fix one or two and they allow the rest to be cleared.