I have Windows 8.1 64-bit OS running on 64-bit architecture. I am installing a fresh copy of Oracle 12C, means I haven\'t installed any version before on my system.
Looking at Oracle's support site, it could be one of two things (may be #2 in your case, but including both).
Problem 1:
Enable administrative share for C$ (Please check with your System Admin to do this or See Microsoft document http://support.microsoft.com/kb/314984)
Check that it is ok:
Retry the installation
Problem 2: Remove the OracleRemExecService before doing the Oracle Client 12c Release 1 32-bit or 64-bit installation on the same Microsoft Windows x64 (64-bit) after installing the Oracle 64-bit or 32-bit software .
( This service is having a intelligence .Once someone tries to stop it this service gets deleted. This is due to the fact ,that this service is not running from the Oracle Home like other oracle services ,but from temp . For example : C:\Users\AppData\Local\Temp\oraremservi... )