1)
Safe mode
http://support.apple.com/kb/ht1564
This will not load any 3rd party additions, it will load some more conservative Apple drivers (may cause screen flicker), and it will clear some kernel caches (a cache is saved data in a form that can speed up a program, but is totally redundant to the original source, and thus can be safely cleared). Booting into Safe mode is just an experiment, but can frequently eliminate any 3rd party interference, or a cached item out-of-sync with the world. (Verify Safe mode via Applications -> Utilities -> System Information -> Software -> Boot Mode -> Safe vs Normal)
2)
If Safe mode work, then...
See if you have a panic report (file's ending in .panic). If you have more than 1, please post a couple as the differences can be very useful:
Look for the Kernel Panic reports at:
Finder -> Go -> Go to Folder -> /Library/Logs/DiagnosticReports
<http://support.apple.com/kb/ht2546>
<http://support.apple.com/en-us/HT200553>
The panic report should have ".panic" in the file name.
You can put the panic report in an "Additional Text" box when you Reply