Did you record in Multitrack or Waveform view? If it was Waveform view, you've almost certainly lost them unless you specifically saved them - but if it was Multitrack, and you've just got blanked out spaces where they were, then they may just need re-linking. If you highlight one of the clips and go to the Clip menu, at the bottom there's a line that says 'link media'. This should help you re-locate it.
It's generally safer recording in Multitrack view, as files are written directly to disk, and can generally be recovered - but not always. It rather depends on what caused your computer to crash. Waveform view records to a temp file, and in the event of a crash, there's a much lower chance of a successful recovery. Once again, it depends on what caused the crash.