Should I
format Hard Disk with
NTFS System?

I have
Genuine Windows 7 64-Bit installed in my PC. But my Computer guy says it has
virus so it is needed to be formatted.

So if I format Hard Disk and again install same windows (
same product key) will it work?
And Will Genuine Windows 7 64 -Bit Dvd will work for formatting the hard Disk?
Plz reply it quickly. I m waiting for ur advice.
Thanks in Advance