[HM] lost system folder!

[michaelP]

Hi folks, given a bit of crashing recently, I used a free version of 
TechTool to repair the desktop, etc. Having restarted the mac
(automatically) I noticed to my horror that the System Folder was no longer
visible on the internal hard disk! In using Find (for system, etc) it finds
such files but the System Folder and eveything under it are greyed out. On
attempting to do Shutdown (in case that would solve the problem, sometimes
it does...) I received a terrifying warning that because there is no "valid
system folder" it might not be possible to restart the machine! So, although
apllications etc seem to work (and thus the System Folder and its contents
must exist) I am stuck with a non-visibl System Folder (e.g., I have another
problem because I now no longer have access to control panels and the Apple
Menu no longer has any components except the "About This Mac", etc).

Does this ring a bell with any of you?

regards

michaelP