ok , i think i know why this happened..
either.
1. he belived he hadnt touched Sys (the bootable partition) when editing..so by a mistake it went along with the reboot.
(if you ever saved your rdb settings then u could just load it up and your boot would be ok again)
2. that you have heard so much about pc lately and you belived that amigaos also could resize a partition without loosing data etc.
that wont work, either u remove it totally or let it stay , also as an extra info must be that when u do this on a pc then the disk will be very fragmented and should only be used if you have no other alternatives..
good luck, and i hope you have a rdb file or a floppy disk with os3.9 recovery so that you can boot your system and start installing again.