Setting up MacMini 2009 with OSX 10.10, and more

After receiving a new set of new memory module (benefit of lifetime warranty), I started setting up my MacMini 2009 with clean installation on the internal 160Gb harddisk.  The process was pretty straight forward, and at the the I have OSX 10.10 running properly.

But my main goal is to run bootcamp on it, so I shrinked the size of the OSX partition down to 50Gb, which should be enough to do basic stuffs.

Then I want to set up bootcamp, however, BootCamp detected that my MacMini 2009 can only run Windows 7, and I don't have the disc with me.  Windows 7 on thumb drive DID NOT seemed to work, so I have to wait until I get home before I can try that part of installation.

Next I wanted to set up OSX 10.10 on an external harddisk, so that can install as many apps as I want, as my internal 50Gb partition is just not enough to install all the applications that I care.  There was a previously installed OSX 10.10 partition on my external harddisk, so I thought I could just reuse it.  Well, bad idea, because that one ended up has some strange problem.  The biggest problem was that App Store on that partition failed to work at all.  Without that working, I can't download apps, and not even update the system.

So I looked around online, and found various people suggested various ways to solve the problem, but none of them worked for me:

• Reset PRAM: did not work.  I couldn't even get that reset PRAM thing working.  After several trial and still couldn't got the "second restart" step happening, I gave up.
• Killing certain processes in activity monitor: tried, and couldn't find both process that was mentioned in the forum message.  
• Restart : didn't work.
• Reinstall a clean OS: did NOT work.
• Set DNS to use Google DNS: doesn't work

However, at the end, I solved the problem in a very stupid way: I selected "Enter Full Screen" from the menu, and suddenly the AppStore page start showing up, and I was then able to download software form AppStore.