.. if this is the client, as long as you shut-down windows properly (didn't just pull the power, but went to start->shutdown in the windows start menu), then it should be fine.. open up [fah root folder here]\unitinfo.txt.. should tell you how far along its gone through its current work unit, and will read as 0% done if it had reset everything.
is this the first time you have tried starting it since renaming? try renaming it back. then navigate to the folder, execute
./FAH502-Linux.exe
assuming you are using version 5.02. if that doesnt work, i dont know, you may have lost the work unit. but the work is still there, you should be able to continue with it.