powerbook G4 won't boot up properly

Hello,
Yesterday i installed Ice Clean and ran a few of the maintenance procedures. This morning when i tried starting my laptop, it started with grey screen and apple symbol, then black screen with white text stating;

Mar 13 08:02:44 launchd: can't exec /bin/sh for single user : no such file or directory.

Please help! I tried contacting Ice Clean, they claim it is not related.
I checked my system profile and i thought i had 1gb of RAM it only says 512gb. could a RAM failure cause this problem?

Have started using target disk mode with my old faithful G4 and everything on the hard disk is still intact. Ran disk utility and all ok!

Thanks for your time.

Checking RAM

Hi, I've just removed the cover and i have two 512mb cards installed but only one is showing in system profiler. Are there precautions when removing and re-installing?
Thanks for your quick response.

RAM Failure?

Hello, Have checked the RAM, removed and re-installed. Ran the hardware test and it tells me i have one empty slot! Which is not the case, unless i'm seeing double!! So after a quick test apparently there is not a problem with Memory. (I'm guessing it is only recognising the good memory card.)

If i re-install OSX i only have an older version so is an "archive & re-install" O.K. I won't lose any files??

Thanks again, i'm in quite a panic as i have to perform with my laptop tonight!

Regards
Micart