simrantogether,
Whomever is having problems could try clearing their browser cache. It may work, though I suspect that their ISP is caching the content before passing it on, in which case you will most likely have to wait on them.
The website displayed the Plesk default page for only a very short while before the vBulletin pages were back. If it were truly not accessing the site, you should receive either a 404 error report (missing page) or a Failed DNS Lookup report (unable to locate site).
Honestly, it is just a guess as to what is happening.