Make sure launcher.exe and swtor.exe are part of your safe list on your antivirus / firewall.
Try to run a repair. Steps are:
Non-Streaming launcher - Log into the launcher but don't click Play. Check for small letters "ST" in the bottom left corner. If this is NOT present, click the cog icon and then run the repair option.
Streaming launcher - If the letters "ST" is present, close the launcher, right mouse click on the game shortcut, select open file location and delete the BitRaider folder. Then start the launcher.
Make sure launcher.exe and swtor.exe are part of your safe list on your antivirus / firewall.
Worse case scenario switch to the non streaming launcher if your on the streaming launcher:
NOTE this is a complete download of the game again
right mouse click on game shortcut and select open file location
open the launcher.settings file in notepad and locate the below line and edit to the below
, "PatchingMode": "{ \"swtor\": \"SSN\" }"
, "bitraider_disable": true
SAVE the changes.
Delete the BitRaider, Movie and Asset folders then start the launcher.
I do not take credit for these steps, these are just what I found in the swtor forums from other users like Owenbrooks.