Yeah!!! Big problem
Yes,
formatting your hard drive frequently can have negative impacts on it. Your hard drive will die much too earlier than it normally should. Formatting every 1/2 - 2 years is recommended.
As for viruses affecting your computer, it's solely your fault. Viruses can't come from nowhere.
1.Stay away from unsafe sites.
2.Always keep your anti-virus' real time guard ON. Also keep the signature up-to-date.
3.Scan your computer in Safe Mode, if your anti-virus can't fix some virus in Normal Mode.
4.Use an anti-spyware and a firewall along with your anti-virus to add to your computer security.
5.Keep your Windows updated, with all the security fixes from Microsoft.
6.Don't download unknown software
Cheers!!!