IMac hangs several times a day

Question

I have problems with my imac (late 2012). The iMac hangs several times a day. The messages (console) are different. 
For example:
03.09.13 13:06:24,465 spindump[1969]: firefox [1056] didn't gather any samples due to audio running 
03.09.13 13:11:15,087 Safari[400]: CGContextClipToRect: invalid context 0x0
03.09.13 13:11:15,173 fseventsd[61]: SLOWDOWN: client 0x7ffe5c827000 (pid 1254) sleeping due to too many errors (num usleeps 15)
03.09.13 13:11:16,280 Safari[400]: CGContextClipToRect: invalid context 0x0
03.09.13 13:11:18,079 Safari[400]: CGContextClipToRect: invalid context 0x0
03.09.13 13:11:35,371 com.apple.launchd.peruser.501[171]: (com.apple.mdworker.shared.04000000-0000-0000-0000-000000000000[1937]) Exited: Killed: 9
Does anyone know a reason?

Answer 1

Back up all data immediately as your boot drive may be failing.
If you have more than one user account, these instructions must be carried out as an administrator.
Triple-click anywhere in the line below on this page to select it:
syslog -k Sender kernel -k Message CReq 'Channel t|GPU D|I/O|Previo' | tail | open -ef
Copy the selected text to the Clipboard (command-C).
Launch the Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
Paste into the Terminal window (command-V).
The command may take a noticeable amount of time to run. Wait for a new line ending in a dollar sign (“$”) to appear.
A TextEdit window will open with the output of the command. If the command produced no output, the window will be empty. Post the contents of the TextEdit window (not the Terminal window), if any — the text, please, not a screenshot. The title of the window doesn't matter, and you don't need to post that.