No virus can prevent you running the recovery software from any point, including before Windows boots up. You just hit F11 when prompted during boot up and you're into Aro**is, which gives access to an entire image of your hard drive, with all of your personally selected installed software, from which you can restore said hard drive back to pristine, uninfected, everything-installed perfection.
haha .... thanks for the laughs ....
Rule 1
Never say never when it comes to viruses. Display arrogant beliefs ("No virus can prevent".... yeah, right !) when it comes to computer viruses and sooner or later it'll come back to bite you in the backside.
Rule 2
A backup system which is reliant on storing backups on, or the restoration process is dependent on the very device you are backing up
IS NOT a backup system.
In summary, you have been very, very lucky with your computing so far.
Learn how to do backups properly or don't bother to do them at all. You should be backing up to multiple external devices of sufficient robustness (i.e. you can rule out USB flash drives and the like right now).