Setting Rocket League to run as an administrator can help in cases where Rocket League isn't starting.

 

Here's how to run Rocket League in Steam as an administrator:

1. Open Steam
2. Click on the Library link along the top 
3. Right-click on Rocket League
4. Click on the Local Files tab
5. Click on the Browse Local Files button
6. Double click on the Binaries folder
7. Double click on the Win32 folder
8. Right click on RocketLeague file
9. Select Properties
10. Click Compatibility tab
11. Check Run This Program As An Administrator
12. Click the Apply button
13. Click the OK button

You should also run Steam as an Administrator:

1. Right-click on the Steam icon on your desktop
   or Navigate to your Steam folder and right-click Steam.exe
2. Select Properties
3. Click on the Compatibility tab
4. Check Run This Program As An Administrator
5. Click the Apply button
6. Click the OK button