sounds like the kernel is booting, but it can't access the / filesystem...
maybe check your bootloader's config, probably
isolinux.cfg or something...
also, make sure your kernel has built-in support for the filesystem your ramdisk or whatever is using... it has to be built-in support, not a module (unless you use an initrd)...
sorry i can't be more specific, i don't really know how the slax build scripts work...
just my

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