Checking MarketPlace Connect installation on Magento 1.x
If you believe the plugin to have been installed, but the plugin menus for managing listings etc. are not showing in Magento Admin follow these steps:
1) Check this file:
You'll see this.
If it says false, then change it to true and save the file.
If it already says true, flush the Magento cache (which is in system>cache management>flush magento).
If the file isn't there, then the plugin needs installing.