Problems with iMac after installing Snow Leopard

I went to install Snow Leopard the other day and left it to install for a while. When I got back it looked as though it had rebooted the computer during the installation and when I went to operate it I found a few problems with the system:

1. The Snow Leopard program didn't seem to install onto my computer even after a second installation.
2. My magic mouse was having problems for example the finger swipe to scroll up down or across was not working.
3. The computer would not go into sleep mode - both automatically and manually.
4. The Expose function/button was not working so after changing the system preferences for it, it seemed to mess up the rest of the f1, f2, f3 etc. keys so now the volume, pause/play and next track buttons no longer do what they are supposed to.

I have tried restarting the system etc. but nothing seems to work.
Can someone please help me with this?

G'day and welcome to the forums.

Well for starters how about some info on your system? Intel, PowerPC, full retail install SL discs and not a system specific or upgrade version? Very hard for anyone to help with so little assistance.

Hi,
I'm not a computer whizz so all I can tell you that I know is that it is a Macintosh HD version 10.6.

One more thing to add;
I have been experiencing buzzing lines that ravel up the screen lately as well as the other things.

I'm not sure what has happened but it seems as though Snow Leopard corrupted the system or something.