Computer Data Loss is unpredictable, causes include accidental formatting or deletion, hard disk problems, virus, computer software glitches, computer boot failure and others.  Commercial data recovery costs vary; a do it yourself recovery may appear to be cheaper, however, unless you are confident you should not experiment in the midst of problems. (You would normally learn to swim before jumping into the deep end of a swimming pool).  No matter which way you go - you should stop using a problematic hard disk to prevent further degradation (if you can not remove the drive, stop using the computer).  

Do it yourself recovery:Commercial and shareware software is available to assist in recovery tasks, make sure that you follow instructions carefully so as not to introduce additional problems. Refer to DIY Recovery  link for considerations.

PC Repair Service  many PC maintenance facilities can perform data recovery, they use the same software you can buy yourself.  PC Repair link provides suggestions for evaluate their services.

Data Recovery Providers specialize in data recovery. Most use specialized tools for recovery. Some have clean room facilities to allow then to open and repair the internals of a hard disk.   

HDrevive is a local data recovery specialist offering cost effective services to consumers in the Bay Area.  We have a no-recovery / no-charge policy.  The HDrevive Method  link describes our process and methods we use for  Data Recovery.