You need to find your current file. Quickbooks has defaulted to it's standard set up. To find all of your quickbooks file do a search for .QBW files. On XP you can find the search on the windows tab. Search for all files that have.qbw in the name. Once you find all of them, note their locations and date of last access. (the lastest date will be the old file since Quickbooks opened that one up. What you are looking for is the file accessed right before you put in the new power supply.
One you find that file, wirite down the location and then open Quickbooks. Click on open file and then browse to the location that you wrote down. Click on the quickbooks file to open it. This should be your most up to date file and you should be good to go.