It would help to know what version of OpenAccess are you using?
But if you are using a recent version then probably the reason for you not seeing the enable project menu items is that they are hidden by default. As Serge explains in his post you can easily switch to the OpenAccess Classic menus and have these menu items available.
About the other issue that you mention, indeed it seems that your Model project cannot be loaded because of the OpenAccess.targets file.
Unfortunately the OpenAccess.targets file is very important for the functioning of OpenAccess. Without it the OpenAccess enhancer will not be invoked which will cause the generated entities and context not to work correctly.
We have never had such a case reported, but it seems that for some reason your user has limited rights for the OpenAccess.targets file or the directory that contains it.
You could check that your user has at least read and execute rights for the directory and the .targets file.
It will help to know what version of Windows are you using on you development PC?
It is possible to have different access rights depending on the version of Windows that you are using.
Also, is it possible that some permissions are applied due to domain policy or something?
Another thing that you could do is try to set UAC to the least aggressive / protective setting.
Looking forward to resolving this issue.
All the best,
the Telerik team