I am pretty sure, you will have to repair multiboot, multiboot-kernel options.
For multiboot you have to have an image for each of the kernels you have installed / want to boot. You better search for the multiboot thread to avoid further issues. You could search for multiboot from the X-Terminal pretty quicklyonce Maemo is up and running.

If you happen to have kernel-power running when things failed, you will not be able to boot via PC command as is in the wiki

Thank you guys i will try it out in a few minuts and then i will let you know if it's fixed or if i have any other problems (hope not so), also do you guys got any tips for me to get Nitdroid ICS on my N900 and to prevent the same thing from happening??

the download site didn't work so i got the files from 4shared, i was going to start with it but i noticed that my n900 battery isn't 100% full so i'll start with it asap

i don't really get those steps on the wiki page of @michaaa62 i already get stuck at step 2 i don't get what they want me to fill in there (/path/to/ part), i already tried to fill in the flasher's location but it won't work

isn't there a how-to tutorial on youtube?? or can anyone tell me exactly and specific what to do??

the name of my vanilla bin i've downloaded is:

rx-51_2009se_1.2009.41-1.vanilla_pr_emmc_mr0_arm

A.J. to start with, you want "combined", NOT "vanilla". Vanilla will erase all your data.

path/to/your/image represents, well, path to your image. For example, on Windows, it might be something like "C:\Users\A.J.\My Documents\" or some such. Similarly on Linux it might be "/home/A.J./" etc.

There are lots of tutorials around. On Youtube as well as on this forum. Do not be afraid of the Search button.