It looks like openerp gets an error trying to install the modules. You should check the logs to findout where the problem is (dependency on openerp module ? dependency on python package ?).

When a module stays in 'to be installed', you can select them and click on the button 'Cancel install' (where before the button 'Install' was).

Did you get any errors when you tried to install the module(s)? Have a look in the log file, there is probably a message about what went wrong.

Please check all the dependent modules are there in your addons folder.

I have the same problem with addons from camptocamp and akrition

Like Omal suggested make sure you have all the dependent modules already installed. You can open __openerp__.py file to check the dependent modules or you can do the same under the Dependency tab inside the module in webclient.