It probably stopped booting becuase a zip drive is not a usb flash drive. You need to use the non-usb version of NASLite+ since a zip drive will look like a hard disk to the operating system and it will use different drivers and device names to access it.
I posted instruction on how to get NASLite+ to boot off an ide hard drive in the NASLite+ forum. It should also work for a zip drive. Just skip the partitioning directions
As a quick test to see if you can boot from the zip drive, try typing
sys d:
where d: is the drive letter of your zip drive. That will make it bootable to a minimal DOS system.
If you can boot from the zip drive after that, you should be able to get it to boot the non-usb version of NASLite+.
Let us know if it works or if you have problems.