There's a few threads on this forum about installation help, plus Frontier's
own support you can contact if you get really stuck.
Does the Elite Dangerous launcher appear at all?
Does Steam log you into the Elite Dangerous launcher correctly?
Does Elite launch when you click "Play?"
Did you change any in-game networking settings the last time you played?
Steam launch default
Steam allows you to set some defaults which you can set in the Steam game profile, under "General" - say you accidentally selected VR as the launch default, but you don't have VR hardware.
Persistent files
You can try renaming (or move) all of the Frontier directories under "yourUser" profile: -
Code:
C:\Users\yourUser\Appdata\Local\Frontier_Developments
C:\Users\yourUser\Appdata\Local\Frontier_Developments_Ltd
C:\Users\yourUser\Appdata\Local\Frontier Developments
C:\Users\yourUser\Appdata\Local\Temp\Frontier Developments
C:\Users\yourUser\Appdata\Roaming\Frontier Developments
....just put .old on the end of each, then go back to Elite in Steam and run a verify. This should re-run the install script.
Wait for it to finish, and when you run Elite again, it will be as if you are launching for the first time, and you will have to get a login token for the launcher/browser again.
This will only have basic settings, but you can copy your key binds back later.
Connectivity
Elite Dangerous requires access to servers hosted in Amazon Web Services, so any security software you use, your internet provider, (and VPN service if you use one,) must allow connections to various parts of AWS. If this is the problem, contact your internet provider first, and see if they can help.
Edit: Also forgot - IPv6 can cause problems in certain parts of the world. Disable it!