plm, I don't know exactly because I never use precompiled kernels as bare.i, but obviously the following has happend:
since both the bare.i and your downloaded kernel source were the same version 2.4.20, the "make modules install" step has overwritten your original modules in /lib/moduels/2.4.20. So it is not sufficient to reinstall the vmlinuz rsp. bzImage, but you must also reinstall the modules from the Slackware CD. I guess, a installpkg of the bare.i package should do this (but I am not sure, I always use my own kernels).

As for your unsuccessfully compiled kernel: are you sure you configured correctly the modules you need ? I would guess, something went wrong in the "make config" or "make menuconfig" step. Should be not too difficult to get it to work.

i used xconfig, and i read the help for every module and option in the configuration, butt it's very possible to have missed something.

so i use installpkg bare.i? i actually didn't install this bzImage this way. i only copied it from the cd?! i'll try this right away. and be right back to you.
if i post my configuration file, can somebody tell me if i missed something very important?

You'll want delete the directory /lib/modules/2.4.20 and then use installpkg to reinstall the slackware kernel-modules package (I think it's in the a disk set) from the Slackware CD.

the kernel-modules-2.4.20... in a/ ? okay i'll reinstall it. do i have to reinstall modutils too?

You shouldn't have to as to my knowledge, they're seperate from the modules, just delete the existing modules and reinstall the stock modules.

LSD your the man! everything is back to normal! i'll try now installing the nvidia driver with the slackware kernel source 2.4.20

LSD again thanks for the help and everyone else thank you too!