more than likely you are being a bit paranoid
if the pc is still working fine, then you obviously caused no damage. while it is true that static discharge can damage sensitive parts, simply touching the cables poses very little danger. you'd have to shock a circuit board directly to have the chance of doing any real damage and that is not 100% that you would.
you more than likely touched the case while opening it and even while reaching inside which would have grounded you and prevented any discharge. so more than likely without realizing it, you did the right thing and grounded yourself before reaching into the case.
again so long as the pc is working fine, then you have not done anything to it other than opening it.
edit...