Cgminer not working with AMD APP SDK 2.8
Assuming you are using windows:

uninstall all AMD drivers

Do not install (uninstall) APP SDK.

download 3.11 beta version of catalyst drivers
http://www.guru3d.com/files_get/amd_catalyst_13_11_beta_9_2_(13_250_18_november_7)_download,1.html

Make sure you're cgminer settings are modeset and try again. If you are never on modest cgminer settings, you may never know if your software/driver config will work.