Hey Fjk,
Is it working normal in Safe Mode??
If yes then login the system in Safe Mode and disbale the SEP Service(SmcService).
After that login the system in normal mode and check if it working then it mean that symantec come to freeze it.
So try to cleanwipe tool otherwise use the third party software(revounistaller).
After removing all the symantec dll files clear the folder if it dispaly in Drives.
Reinstall the sep.
Hope this information will help you.