recover lost files

My power cord was wonky. Copied important files into one folder on desktop--checked contents to be sure everything was there--and copied it to my external HD. WEnt to Apple Store. When I got back with new cord, could not find backed up files on ext HD. THey weren't in trash (other stuff was). Not on desktop, HD, ANYWHERE. SO, where did they go? More importantly--can I get them back and how? THese were important and I am sick to my stomach since they appear o have vanished into nowhereville. Please, can anyone help? I tried to do Time Machine to find them, but apparently, it was not on.
MAC OS X (10.5.8) on powerbook.
Thank you

In cases like this the best thing to do is turn everything off. Its crucial not to download or work with the computer because these operations can overwrite the area the files were stored. Then you might consider contacting a nearby Mac Genius bar.

If you are technically included programs like http://subrosasoft.com/software/filesalvage or http://www.prosofteng.com/products/data_rescue.php neither of which I have tried.