Without knowing what process their support performed on your PC, it may be hard to resolve this problem, please provide full details on what was wrong on your PC and what support did on your PC.
Also, when you start your PC now, what is the startup sequence you see, do you see the manufacturers logo scree, then do you see the spinning dots to indicate Windows is starting, and then the login screen, at what point does that process fail, and what error is indicated on the screen.