For those who are curious about which type of problem means what, here's a brief summary of website issues (in between the first and second incarnations of Wintertree, I've been a freelance website designer). Note that these are the most common reasons for these issues; borked DNS entries can produce all many of them all by itself.
If you get "server not found" generally the domain name is completely unregistered. It could be that someone just screwed up and let the registration lapse (as Microsoft once did) or it could be that the company is defunct and let it go.
If you get a domain registrar's parking page, there can be several reasons (some of them dependent on the specific registrar). It could have lapsed but not yet been released. It could have been newly registered by someone else (often a cybersquatter). Or they could have really borked their DNS.
If you get a cybersquatter's page -- a "this domain for sale" thing -- you can be pretty sure that the company no longer exists, or that someone has REALLY screwed up, because the name isn't released for 30 days after it lapses, and if you're a company where nobody is looking at your email or your website for a month, you've got bigger issues than the status of your website.
If you get errors -- server errors, page not found ("404") errors, SQL errors, and just about anything else that comes back as an error -- the odds are that the site, and company, still exist, but someone tried to change something and broke it instead.
Sometimes script errors can make a real mess of things -- Wintertree's first website, back before I even had my own domain name, was at Illuminati Online, and I very proudly wrote a script to swap files around for the "dragon of the day" freebie. Except, um, I had an issue with my Cron job. Instead of launching the script every day, I launched it every SECOND. And it didn't terminate properly, either; it kept copying the day's file, over and over. With a new instance joining in the fun every second. This did not improve server performance! The guys at IO disabled the whole thing and emailed me to tell me to fix my script. :p
So something that involves some kind of script or database error generally means that the company is still there, but they've munged something in some way, and the site will be back and working correctly as soon as they've fixed it.
One thing that makes me edgy, actually, is a perfectly normal-looking website with news or other dated material that hasn't been updated in a year or more. If a company is putting out regular news about, say, new releases, and then they suddenly stop, you don't really know what's going on. It may be a "zombie site" where the owner has paid the domain registration and hosting fees for a few years in advance, and the company doesn't really exist anymore. Or it could be just fine, but the only guy who knew the server password quit and nobody even knows who to ask about fixing it. Or, in the case of one of my clients, the registration was actually owned by another person who was holding the site for ransom!
tl;dr
domain not found : dead
cyber-squatter : dead
parking page : almost certainly dead
script/SQL/file error : probably alive
not updated : anybody's guess
