Three things to try.
1. See if username and password still work from their webmail (if they have any).
2. Check the account settings - although it's VERY unlikely they fail all all three PC's at the same time.
3. Contact their customer service. A 'server error' is something with them, after all, not with you.
I have read about this problem occurring on several occasions before, but not seen a response reported that cured it. My apologies if I raise it once again (hopefully, this time, for a successful conclusion to MY current problem). I live in the United Kingdom, in Pembrokeshire, Wales, and my ISP is 'Talk Talk' (originally I used 'Tiscali' which was taken over by 'Talk Talk' Internet Services some time ago, but have had no real problems with either provider in the past).
A few days ago our three household computers blocked email facilities - in and out - suddenly, all at the same time. They are wirelessly linked to a British Telecoms phone line through a common router. I get the onscreen message reading, "Logon - pop. tiscali.co.uk" in a pop-up window each time I try to receive or send mail. The window asks me to enter username and password. These are both shown correctly, but even if I re-enter them the window returns to my screen almost immediately. The larger Outlook Express process window tells me that I have a problem logging into my mail server (as if I DIDN'T already know!), and tells me that I have password rejection due to, "No, Server Error: 0x800CCC90, Error Number:0x800CCC92". I've tried a System Restore change - it made no difference to the problem, as did re-entering the mail set-up details. I've also shut down and disconnected and then reconnected the router. The problem seems to come from outside of the computers, or something that affects each of them concurrently.
I am running Windows XP, using OE6 and IE8 as my main email and internet provision. I also run Firefox and Google Chrome. I've had no problems with my email reception before on my Dell Inspiron 1300 laptop, which is about six years old but gives me little in the way of problems. I also have a desktop PC (a Fujitsu Seimens Scaleo L running XP Professional) and my wife has a brand new laptop (an Acer Aspire 5742Z running Windows 7). The other two computers also have links into OE for email service, though the Aspire runs it through the updated Windows 7 programme. I am happy to run OE6; I'm used to it and it gives me what I require. I also don't want to go through the hassle of a change of address and advising friends and family of a change. I'd be very grateful for some advice and help with this problem, please. Thanks, folks!