Have a 1990 Lexus LS400 the ignition won't turn and the alarm is sounding when the battery is hooked up

call your dealer

if it has an alarm hook up the cables so the alarm goes off then deactivate it with the remote. if you dont have the remote then you need to take it to an alarm shop and get a remote programmed for it if they cant they will have to remove the alarm and you will need to get an aftermarket alarm for it but yea it wont start because the alarm was on. when you try to jump a car with an alarm even if you have the keys in the ignition the alarm will go off its a fail safe so noone can jump your car to hotwire it. but just do as i said jump it and disactivate the alarm with remote and it should turn over with ignition......
one thing you can try close all the doors lock the doors.....USE YOUR KEY TO LOCK THE DRIVERS SIDE DOOR AND THEN UNLOCK IT. See if this might reset it.....
Best of luck i hope this will help

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this could be a starter or the enigtion swicth yes if you crank the key to long it will kill the battery.

yer right,,,its a dam lexus??? there nothing but problems when they go wrong,,, not that they go wrong often, but when they do??????
i realy cant think of a way you could do what you wont to do,,,,, but i can think of a way to put it right, take it into the lexus dealer they will fix the alarm for you,,,only one thing that springs to mind is when did you last change the kye fob batterys?????
however when you do change them do it very very fast,, or you lose the coad for the alarm???
then it wont go at all,,, its a lexus!!! yuck!

Your keys are prob. worn. My car did the same thing until i got very expensive new keys made.

It sounds like your battery is dead. Try recharging your battery:)

My 1991 Lexus LS 400 does something similar. When the alarm goes off I use the key to unlock the passenger side front door and it turns the alarm off. Go figure, I know it sounds funny but it solves the problem for me.

bad ground or blown fuse