Unity not working after update

Hi there,

I am new to Unity and started learning a few months ago. I downloaded the Unity 5 version. I started working on a small 2D game last month. A couple of days ago my computer crashed and I had to reinstall my windows and this time I installed Unity 20. But while installing Visual Studio was not installed and displayed error. I tried couple of times. Then I tried installing VS code offline and did that successfully. I selected code in the editor window of unity. I can edit my scripts but when I try attaching scripts to gameobjects it displays error stating some issue with class. I checked the class name and the script name, both are same. I even tried creating a new script and adding blank script. the result was same.
Additionally I am getting 2 blank errors on console window, that has just the time stamps, no details and another one that says "Code Coverage collection is enabled for this Unity session. Note that Code Coverage lowers Editor performance."
Could someone help me identify the real issue. I am in middle of nowhere.