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!