Hi,
1. Download the install package on our website again and install it on yours. That should fix that issue.
2. This means that the processing of the page is stopped in the middle. It could be anything: a bug somewhere, in HikaShop or not, a memory or execution time limit of the hosting, or a security component.
I would recommend turning on the error reporting and debug mode of the Joomla configuration so that next time you reproduce the problem, you'll see the error message instead of a completely blank page. The error message will help you (and/or the developers responsible for the place where you have the error) understand what's going on.
Normally, these errors are also logged in the PHP error log of your server, so you (or your hosting) could check on that in order to find it.
3. HikaShop and none of our software have such function.