That's why you need to recognize what is the legal and normal processes running in Task Manager. Anything strange, you can google it to check owner.

The problem with virus when in C: or where OS is running. Usually nothing in D:, which is normally to store data, is running. Only running applications call the data. So, virus in D; will not be activated.

I would just format C:. Install anti-virus first and scan D:. After everything okay, install all required software.

When you press Ctrl+Alt+Del you can select Task Manager. There you can see under processes what exe is running. If yours is still fresh install will all necessary application, you can observe what is running there. If in future you suspected some virus, you can see there and see if there is any exe that is not familiar to you. Then you can confirm what the file is by Googling.

Some people with limited space on C: can also install application on D: This way you need to format both, No choice but to back-up your important data. My friend when done all the necessary installation, create an image of the HDD. That way in case he need to reformat the whole thing, he can just reinstall the image. Must faster this way and everything back to familiar setting. HDD is not expensive nowdays