As the title suggests, there are always folks that have problems downloading and playing in the PTR, and 5.0.1(4) will have no exceptions. Currently, if you have access to Pandaria Beta, you are not able to log-in to the PTR for reasons assumed.
*Previous Post on PTR Notes and Live Info
However, for the folks that aren't sure how, here's a little tutorial:
1. Go to the Character Account [Copy} Page in battle.net:
a. Now copy the character you would like to mirror (play on test)
2. While that is processing (a few minutes to an hour max), you will want to download the PTR:
3. Depending on your internet speed, you might just want to go do something outside.....like ride a horse, go fishing, shopping, or swim with the sharks.....
4. Now open your WoW Launcher and go to Public Test (PTR):
5. Enter your Account Information, password, and add your Authenticator.
6. GO PLAY PTR! AoE loot! And all the other goodies you can getcha hands on!
7. Wait two weeks for release date announcement
8. Go to gamestop, WalMart, Amazon and pre-order your Collector's Edition (or just use your battle.net bucks to purchase auto download with all that cash you raked in from D3 RMAH!
9. Stop reading this. You are done. I have nothing else to say.
10. Really? Why are you still reading? Oh. You are having issues. Holler in comments and I will walk you through it. =)
There was just a comment left about WoW1 and WoW2 access. Here are the screens that are showing WoW1 is locked out for Beta users: