Can I reset the crash alarm geber on 1994 540i-sedan bmw

Quite often people forget to attach the ground cable that goes under a bell housing bolt , check there first.

Hi it seems like key is not responding. Its been immobilised.
you need to get some one down to get the key to be read by the car. Possibly need the car key reprogram

Check you have not left any wires off or trapped any when putting gearbox back in

One problem can be when changing batteries be careful not to push any buttons, this can cause problems or if the batteries have been dead for a while, looses its "frequency" the alarm in the car is not picking up the transmitter in the key.(key and alarm in car out of sync ) get the keys re-coded. depending on which bmw you have you can DIY ( google re-coding bmw 5.. keys) or go to bmw.

please how do i reset my alarm my car is frozen

The alarm usually has it's own battery. Find it and disconnect it.

disable the hood microswitch. just unplug it. That and the cabin sensor are the most probably reasons the alarm will go off.
Alarms are useless. Totally effin useless. So it goes off.....then whaddya going to do. Shoot someone? Call the police? or listen to it drain the battery over and over again.
But....you can't disable the alarm totally. The bmw engineers have tied it into the main computer. you can however disable the sensors one by one so it doesn't set off the alarm. Hood sensor....Hood sensor....that's the culprit.

batterys in the remote??

You car should have a harnas already installed. Sigma and stellar alarms are easy to fit according to pro's. visit bmw e36 blog for more details.

there should be a sensetivity nob on the alarm box itself turn that down and your problem should be solved if not just invest in a new alarm.