To restore chimes, go to System Preferences / Sounds.
If you keep losing settings like sound, reset the PRAM:
- Shut down your Mac.
- Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the Command-Option-P-R keys before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
After resetting NVRAM or PRAM, you may need to reconfigure your settings for speaker volume, screen resolution, startup disk selection, and time zone information.
Excerpt from: http://support.apple.com/kb/ht1379
Suggest you try reseating the memory modules. But I cannot help but wonder if one of them has just died - an ailing memoy stick would explain the previous kernel panics.
Thanks for that, at least have a better understanding of what might be happening, Alas, still no chime. The Mac is unmuted and I can hear other other sounds eg: trash crunch etc. from internal speakers.
Tried the 4 keys PRAM reset, but after switching on then holding down, it just seemed to switch on and off several times and I never got to the grey screen.