On my MBP 17 (2011) I run Lion. Since a week or so I have got this weird sound problem, which is already described in this forum: After booting sometimes there is no sound hardware in System Preferences. When I reboot the sound hardware is found sometimes, sometimes not. I tried all solutions offered in various threads, like safe boot, resetting PRAM, SMC, Audio-Midi Setup etc. and no, there is no red light in the headphone jacket. But no success.
I'm still convinced it is a software problem with Lion. I bought the MBP 6 weeks ago.
Now I think it's a good idea to re-install Lion. But I don't want to lose my settings, programs, documents and data. My question is, how can I do this. I have a DVD with Lion on it available.