Open console in Applications>Utilities, check the system log for the date/time of the last problem & the Startup right after that for clues.
See if the Disk is issuing any S.M.A.R.T errors in Disk Utility...
Open Activity Monitor in Applications>Utilities, select All Processes & sort on CPU%, any indications there?
How much RAM & free Disk space do you have also, click on the Memory & Disk Usage Tabs.
Open Console in Utilities & see if there are any clues or repeating messages when this happens.
In the Memory tab of Activity Monitor, are there a lot of Pageouts?
There was also this, I dont know iwhat it means, but it was open in console saying there was a crash.
Process: Google Chrome Helper 
Path: /Applications/Google Chrome.app/Contents/Versions/26.0.1410.65/Google Chrome Helper.app/Contents/MacOS/Google Chrome Helper
Version: 26.0.1410.65 (1410.65)
Code Type: X86 (Native)
Parent Process: Google Chrome 
User ID: 501
Date/Time: 2013-04-23 23:16:45.546 -0400
OS Version: Mac OS X 10.8.2 (12C3012)
Report Version: 10
Interval Since Last Report: 399335 sec
Crashes Since Last Report: 1
Per-App Interval Since Last Report: 27407 sec
Per-App Crashes Since Last Report: 1
Anonymous UUID: CF621CD3-E30E-ED90-A273-68FDDFDD3437
Crashed Thread: 0 CrGpuMain Dispatch queue: com.apple.main-thread
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Application Specific Information:
Application Specific Signatures:
Graphics kernel error: 0xe00002be
One way to test is to Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, Test for problem in Safe Mode...
PS. Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive
Reboot, test again.
If it only does it in Regular Boot, then it could be some hardware problem like Video card, (Quartz is turned off in Safe Mode), or Airport, or some USB or Firewire device, or 3rd party add-on, Check System Preferences>Accounts (Users & Groups in later OSX versions)>Login Items window to see if it or something relevant is listed.
Check the System Preferences>Other Row, for 3rd party Pref Panes.
Also look in these if they exist, some are invisible...