its possible that if your external drive was being accessed during the power faliure it may have been wiped, use some partition management software to see if that detects it as unallocated if so then it needs to be re-formatted in the file system in which your system uses e.i. NTFS for windows xp and after in order for it to be detected.
that being said your data is not completely lost as there are many data recovery softwares that can recover data even from a re-formatted drive
also is there power to the external drive as it may be something simple like a blown power supply?
you could also try taking the eternal hard drie apart and connecting the HDD direct to your motherboard as you may have fried the control board in the caddy