I have a 2820, originally with 3.2.1 , I have upgraded to 3.5.2 and then to 3.7.3 as per instructions, but now the 2820 will not connect to the internet; WAN1 status continually reports "PPP Shutdown". all settings are checked and correct. ISP is BT. Please help !!!

did you use the .all or rst?
I know if you log a case with draytek they will advise the firmware upgrade again using the .rst and then re-configure the device from scratch (if you used the .all that is)

could you put up a screenshot of the wan - internet access - WAN1 page and maybe wan - general setup? (i guess censor any account details ) Also the online status page would be useful - PPP shutdown signifies that ADSL is working and it's found the PPP server so it's probably just a router setting that didn't move over to the new firmware very well that's either not allowing it to connect or is making it drop the connection.