Please stop beating on your desk !!
What do your desk ever do to you !
LOL --OK ahahahaha

Every time that you "bump" your desk and rattle your apple,
you run the risk of doing damage to your HD.
I`ve done the same thing (now I`m on my 3rd HD )

Good news is that there super easy to replace and getting cheaper by the minute.
Bad news is that if you don`t have a "blessed system folder" backed up , it could mean alot of work getting back to normal.
I have had just about all the things happen to my iMac that you have , weird screens, missing stuff ect. all signs of sectors going bad and HD failure.
If you have a back-up device , I suggest that you do that to save what you have.
Then run a test utility to check your HD (be careful of Norton 6.0), and if need be install a new HD get your system to the minimum that you need (no games or excessive stuff) and use Apples "first -aid" and if it checks out in less than 10 seconds then you should be A-OK and have a "good system folder" .
Now drop the whole thing to your back-up device and save it as your "back-up" and then the next time you have you rebuild or format your HD you can boot from that saved folder and then "drop" it on a newly formated HD
At least it works for me, some folks say that a reinstall is the only way to go , but if you have a "blessed system folder" you can "drop" and be all set.
jedi
