As I mentioned above, it’s likely to be a DNS issue. I explained this in a bit more detail in the post I linked to:
If you’re running Windows 8 or 10, there’s also a workaround here which forces your computer to use a public DNS server, such as the one supplied by Google.
This should resolve itself in due course, but it does depend on your own computer, your internet provider and several other factors. However, I can confirm that system access has returned to normal as of this morning.