Easiest is if you can move the drive so both the good and messed up systems are on the same system.
Boot up ArcaOS on the good partition, change the drive letter of the newly formatted drive to something different then the booted system, lets call it C: and D: with D: newly formatted. Then xcopy the system over.
xcopy /h /o /t /s /e /r /v C:\* d:\
Then change D: to C: and remove the C: drive. Some of this might be best to do from the maintenance shell on the install media.
Otherwise use dfsee on a stick to make an image of the good partition and restore it to the bad system.