I'm not able to boot my Linux normally because during the boot appears a line asking telling me: "INIT :Enter run level"
I write 1 and it tells me "enetring run-level 1->No more processes left in this run-level" and I can't go on.
What should I do without re-installing Linux?

You need to get to a place where you're at a command prompt. Enter another number, like 2. You need to get into the /etc/inittab file and enter a run level there for init. There should be a line that looks like this:

init:X:something else

What you want to do is replace X with a number. I would guess you want to run at 2, depending on what you're using Linux for.

But he needs to know how to get into the inittab file. Run level 1 is "halt". The computer should start normally if a boot-floppy is used. Then one can happily edit /etc/inittab. In my Redhat system, the line is id:3:initdefault, with 3 being command prompt level. 5 is GUI level, if you want it to start directly to the GUI. When this happened to me, my computer wouldn't start and I had no bootdisk. So I used a dos bootdisk with Norton Disk Editor on it and did a text search of the hard disk for the above-mentioned line, then I could change it.
Another way is to download (if you have a computer to use) a tiny Linux on a floppy such as Tomsrtbt or Ramfloppy, boot with it, mount your hard disk and start editing. Have fun! Jim.