The store is on the previous website scirra.com and is indeed slow.
The website is in the process of being moved to the faster construct.net domain, but it is not here yet.
For now, the only thing is to wait, and when some connexions issues like the one you report happens, let it be at the moment and come back to it later, it generally "fixes" itself when accessed at a different time.
If you have further issue accessing the store, consider sending an email to supportquw@scirra.com