when a virus, adware, spyware, enters the system
unfortunately will inevitably remove or modify some files.
Making a comparison with a car accident, if someone has an accident such as a bus trample the remaining Probalan the person in a coma or severe nerve damage is high,
which would leave sequels that will not heal
for example, may be invalid for life.
likewise, the virus can enter the coiling against the computer operating system, ie the damage would keep software but the hardware would follow intact.
now as the operating system is the fundamental part which we can see that interact becomes slow or unresponsive, or rebooted, or crashes, or windows will not load simplente, this is what would happen because the virus has destabilized system
for that there is no other option to reformat, clean or install windows and it is RESTORED to normal