after a power cut i have come to switch on my mac and have no desktop icon for my hd, my hd's there and i can access everything in it through my sidebar but when running a search for folders that i know are in there nothing is found. i have tried going through finder- preferences-general to enable the viewing of hd's on my desktop but it's already on(i switched it off then on again just incase but nothing). if anyone can shed any light on this i would be most grateful as i need my search feature for my work.

I would try creating a new user to see if the problem still exists there. If you see the issue in the other user you then need to reinstall your OS choosing the archive and install option while preserving user settings and accounts. If it doesn't exhibit itself in the second user then your user folder has some problems with it. What you would need to do in this circumstance is navigate to Macintosh HD- >Users->Your User Name->Library->Preferences and then find the preference file for your finder or desktop. It is normally titled "com.apple.(something here)". These files can be trashed or moved to the desktop, etc. If the OS needs that file they will be regenerated and that might fix your problem. Good luck!