I believe if you have Nirvana 1.2 or newer installed, then you need to also install the Cryout Serious Themes Settings plugin here: http://www.cryoutcreations.eu/cryout-theme-settings. I believe it’s required with most (all?) of the themes now.
After updating to WordPress at least 4.4, you need to update to at least Nirvana 1.2 and install the additional settings plugin to restore the theme settings page – this was announced here and here.