Hi,
I will try to explain a detailed "how to" and explinations:
Joomla! Global Configuration - User settings tab
-Allow User Registration - Yes/NO Here IF is YES, your users are able to register to your site, IF no the oposite. YOU MUST USE YES HERE.
-New User Account Activation - Yes/NO If you want your users to activate their account by e-mail confirmation, you must use YES, but VirtueMart developers recomand NO, so YOU MUST CLICK NO.
-Front-end User Parameters - Hide/Show IF you want users to be able to select language, editor, and so on in their account settings, you must use SHOW.
This setting is altering VirtueMart login/logout behaviour.
VirtueMart Configuration - Global tab - User Registration Settings:
Joomla!: User registration allowed? if you see YES green colour, this means VirtueMart checks that setting because needs it to be YES, because it is compatible with that setting, otherwise NO will be red colour, and is not compatible with VirtueMart User Management.
Joomla!: New account activation necessary? IF you see NO in a green colour, it means VirtueMart is compatible with that setting, otherwise your users will be forced to activate their e-mail adress before login. If your users didn't activated their account by e-mail, they will see this error:
E_NOLOGIN_BLOCKED
* Login denied! Your account has either been blocked or you have not activated it yet. Did you not get an activation e-mail and follow the validation link? Try for yourself to experience.
This SETTING MUST BE NO all cases.
User Registration Type:
Normal account creation is most used, because provides all information about your customers: billto info, shipto, and, in some cases credit card info. This is what I'm going to use for my sites. It is most used no matter what payment methood and shipping method you use.
No account creation:
This setting is best for your clients that pay only with credit card. They buy and are not registered in your database, although they must provide credit card information (those fields are required there) for payment processing.
Silent registration type is connected to the letterman or newsletter components that remember subscribed users in their database. This feature is still a work in progress.
Optional registration is as it says. Your users can provide their information or not. BUT for the transaction to be done, they must provide proper information: bill to info, ship to info (for material products), and credit card information if you use this type of payment. This registration type can be used for your friends

Info: You are not a Registered Customer yet. Please provide your Billing Information.
(* = Required)"
despite also receiving an email confirming registration completed.
When switching registration type, you must also modify the user fields behaviour for proper functionality, because they are not yet automatically changed. So in user fields management you must change required/not, visible in account maintenance or not, visible at checkout or not and so on.
In our case here it is possible you have a filed or more that is/are required but are not displayed because of shown/hidden setting of each field.
Now about that paypal, I saw that it is a problem in this topic, you must read paypal documentation.
I hope I was clear this time.
And hostricity, theese settings are used and are working! I know you don't speak chinese, sorry about that (it is friendly speaking).
Regards