No, Windows is not a virus. Heres what viruses do:

They replicate quickly — okay, Windows does that.

Viruses use up valuable system resources, slowing down
the system as they do so — okay, Windows does that.

Viruses will, from time to time, trash your hard disk —
okay, Windows does that, too.

Viruses are usually carried, unknown to the user, along
with valuable programs and systems. Sigh… Windows does
that, too.

Viruses will occasionally make the user suspect their
system is too slow (see 2) and the user will buy new
hardware. Yup, thats with Windows, too.

Until now it seems Windows is a virus but there are fundamental
differences: Viruses are well supported by their authors, are
running on most systems, their program code is fast, compact and
efficient and they tend to become more sophisticated as they
mature.

So, Windows is not a virus…