I've been trying to download my games from gog and I am unable to download anything, not the games, not the extras, and not through the downloader, for any game I have.
I've been trying for a day now, restarted my router, played with my firewall etc. and it's still the same, and I have been able to download from gog in the past, just last month or so in fact.
Not sure what to do.

there's an application called Fiddler, which is a web debugging proxy. This shows you all the web requests being made, and more importantly, the response code and content. You could try installing and running this. This would show you if your web requests are getting through to GOG, or being blocked.

If you do try this and have trouble understanding the result, post a screenshot, or save the output and send it to me and I'll take a look.

What kind of antivirus have you got installed? I know there's one of them which is blocking GOG at the moment due to a false positive. I don't remember the name at the moment though.

Ah, it was Avira. Thread here.

Sorry for the late reply, I had to get some sleep.
You gave me some brief hope, wishbone, as I do use Avira, however it doesn't seem to be the case.
Disabling it completely did nothing, and even restarting with it disabled didn't help, and I never received any notifications from Avira in the first place that it was blocking anything from GoG.

As for wpegg's suggestion, I downloaded fiddler and for any file download entry from GoG in the sessions tab it never receives response data (I assume this is what you are after?). I admit that it is a bit beyond me though and not sure what to do with it.

Sorry to hear it. I was hoping that might help you.

Your DNS cache might be corrupt.

Open a command prompt

type the following

ipconfig /flushdns (there is a space after ipconfig)

Don't worry that command is completely harmless whether it works or not.

That didn't help either unfortunately. I cleared all my web temp files and everything too.

Edit:

Started noticing other problems with random websites no longer loading, with the odd thing being that I could still ping the things that I couldn't access (including GOG's download server).
After a painfully fruitless few hours talking with my ISP and with my router manufacturer, who assured me that my router wasn't the problem, it was infact my router dieing a slow and annoying death.
Got a different one temporarily hooked up and everything works fine.
Thanks to all for the assistance.