Sorry for the necro-thread, but the reply by Syed N is misleading and judging from the amount of views, a common issue. Your Sound Recorder file is stored in your temp directory as a .tmp file with ART at the beginning of the file name, followed by numbers. For example "ART1306.tmp".
I found a webpage that gave the following instructions to easily recover such data. You can find it here: http://www.techsupportforum.com/forums/f217/solved-soundrecorder-exe-froze-while-saving-where-is-file-456820.html
In a nutshell the instructions are:
Open a command window as administrator (Click the START BUTTON | type cmd.exe into the Start Search box | RIGHT-click on cmd.exe | select "Run as Administrator") and paste this command into the screen -
copy "%temp%\ART*.*" "%userprofile%\documents"
Look in your Documents folder for a file with the prefix "ART", around the date/ time of the freeze. Re-name the file with a .wma file extension. Worked perfectly for me.