Symptoms were an unhappy grey looking house in the systray, and any attempt to access the shares resulted in a cryptic message saying "the referenced account is locked out".. Remote desktop to the server worked, as did opening the server console..
Thankfully, there was a very easy fix...
It turns out that the clocks on the accessing pc's have to be 'fairly close' to the clock on the home server.
In my case the Server had forgotten all time when powered down (it's an old server, but then so will be most Windows Home Server v1's) as its ickle watch battery thing has died years ago.
So I used the remote desktop to the server, and brought it forward from 1st Jan 2005, to the current day, and bing, the little house went yellow, and my shares work again.
I had a quick google, and the suggestions for fixing this can vary a lot from unlocking the account on the server, to making sure the passwords still match, to advice suggesting to wait a while, because lockouts can lock you out for a period of time.. thankfully there was even one guy on a microsoft forum that gave the the idea to check the server clock.
So if you've recently rebooted your WHS install, and now can't connect to it.. check the date & time on the WHS via remote desktop, and check if it's correct.
In retrospect, I should have twigged that something like this would happen right from when I realised the server wasn't responding to ping, and checked it to found it stuck at the BIOS saying 'CMOS checksum invalid, F1 to continue or DEL to enter BIOS'. I chose to reload setup defaults in bios & let the system boot.. but I won't take all the blame, Microsoft failed here on usability, a nice message suggesting "Unable to Authenticate User due to excessive time difference between server and client".. would have been a little more useful, than an irrelevant message saying "user is locked out".