From 10yrs of experience my friend. And this method has always worked for me. Also this is what HP has suggested to do. Unless yu are extremely familiar with the different types of viruses , the registries they infect (which can be as many as 20 in some cases), the partitions they infect and all of the other nuances , you can still have a corrupted system even after you "fix" it.
take computer back to a previous day.