Headphones/Speaker issue

[Shelle37]

My dad has an HP Pavillion a6512p Desktop computer.  His operating system is Windows Vista Premium.  There is no sound coming thru the inbuilt speakers unless he plugs the headphones into the jack that's located on the front panel of the computer.  No sound comes thru the headphones when the headphones are plugged into this jack, but this is the only way to get the inbuilt speakers to work.  When he unplugs the headphones no sound comes thru the inbuilt speakers.  My dad uninstalled and reinstalled the drivers already, checked to see if all the cables are plugged in correctly, checked the settings in the control panel, made sure the speaker volume wasn't muted.  But nothing worked.  However, I did notice in Realtek Audio Manager on his computer, the rear panel jack isn't recognized, even though the cable is plugged into that jack.  Of course when he plugs in the headphones, the front panel jack is recognized, but no sound comes thru the headphones, just thru the inbuilt speakers.  I have a similar type of computer (HP Pavillion a6248x) here at home, and my rear panel speaker jack is recognized.  Could the front jack or rear jack be bad???  Could the cable connecting the monitor speakers to the computer be bad??  Or is it most likely a sound card issue or a motherboard issue???

Also, my dad can no longer record any sound either.

He said his computer was fine, things were working, and he stepped away, came back and suddenly the sound wasn't working.