Could be many things, we should start with this...
"Try Disk Utility
1. Insert the Mac OS X Install disc, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu at the top of the screen. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
3. Click the First Aid tab.
4. Select your Mac OS X volume.
5. Click Repair. Disk Utility checks and repairs the disk."
http://docs.info.apple.com/article.html?artnum=106214
Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.
(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)
Then GULP, check for this...
Flashback - Detect and remove the uprising Mac OS X Trojan...
http://www.mac-and-i.net/2012/04/flashback-detect-and-remove-uprising.html
In order to avoid detection, the installer will first look for the presence of some antivirus tools and other utilities that might be present on a power user's system, which according to F-Secure include the following:
/Library/Little Snitch
/Developer/Applications/Xcode.app/Contents/MacOS/Xcode
/Applications/VirusBarrier X6.app
/Applications/iAntiVirus/iAntiVirus.app
/Applications/avast!.app
/Applications/ClamXav.app
/Applications/HTTPScoop.app
/Applications/Packet Peeper.app
If these tools are found, then the malware deletes itself in an attempt to prevent detection by those who have the means and capability to do so. Many malware programs use this behavior, as was seen in others such as the Tsunami malware bot.
http://reviews.cnet.com/8301-13727_7-57410096-263/how-to-remove-the-flashback-ma lware-from-os-x/
http://x704.net/bbs/viewtopic.php?f=8&t=5844&p=70660#p70660
The most current flashback removal instructions are F-Secure's Trojan-Downloader:OSX/Flashback.K.