Sometimes you may not be able to open forms and receive an error 400. This is an issue with your DNS from your Internet Service Provider, but you can usually make some changes to your DNS settings to fix the problem.
If you are connected to the internet with wifi, click your Start button and search for wifi settings.
Click Wifi settings under Best match.
Click Hardware properties.
Click the Edit button beside of DNS server assignment.
Change the setting from Automatic (DHCP) to Manual.
Turn IPv4 to On. Set Preferred DNS to 8.8.8.8 and set Alternate DNS to 1.1.1.1 and click Save.
Try opening forms again.
If you still have an issue restart your computer.
If you are connected to the internet with ethernet, click your Start button and search for ethernet settings.
Click Ethernet settings under Best match.
Click the Edit button beside of DNS server assignment.
Change the setting from Automatic (DHCP) to Manual. Turn IPv4 to On.
Set Preferred DNS to 8.8.8.8 and set Alternate DNS to 1.1.1.1 and click Save.