Can you let me know what OS you have (Windows 10, Windows 7 etc.)
Also make sure you have DirectX 11 or above.
Anyway, try doing the following:
1. Open Steam
2. Go to Library and click Home
3. Click Euro Truck Simulator 2
4. Click Play
5. Select the option Launch with OpenGL (64-bit) and click Play
6. Drive a short distance in single-player and then close the game
7. Restart your PC
8. Open the TruckersMP Launcher.
See if that works.
1. Press the Windows Key + R (Win+R) on your keyboard
2. Enter %programdata% and press Enter
3. Find the folder TruckersMP and delete that folder
4. Navigate to C:\Program Files\ and delete the folder named TruckersMP Launcher
5. Re-install Launcher with admin privileges: https://truckersmp.com/download/ .
Also make sure you have steam open when launching TruckersMP and try launching the game as administrator.
Hope that works!